紅 外 線 光 譜 法(Infrared Spectrometry)

2

紅外線光譜

二紅外線光譜的三要素

一紅外線光譜的基本概念

三紅外線光譜的應用

五傅立葉轉換紅外線光譜儀

四樣品製備技術

3

4

基本原理

紅外線吸收光譜法與紫外線可見光吸收光譜法都屬於分子吸收光譜分子吸收光譜的範疇但光譜產生的原理不同紅外線吸收光譜是振動紅外線吸收光譜是振動--轉動光譜轉動光譜而紫外線可見光吸收光譜是電子光譜電子光譜因此紅外線的光譜和分子的振動轉動分子的振動轉動有密切關係

紅外線光區的波長範圍從 078-1000μm(780-1000000 nm)其波數從 12800~10 cm-1從儀器的應用範圍一般將紅外線光區分為三個區近紅外光區中紅外光區及遠紅外光區近紅外光區中紅外光區及遠紅外光區其波長波數及頻率範圍如表8-1所示IR儀器主要使用中紅外光區中紅外光區

5

一紅外線光譜的基本概念

帶有極性帶有極性((偶極矩偶極矩))的分子發生的分子發生振動（振動（vibrationvibration））就會就會產生產生紅外線紅外線反之帶有反之帶有極性的分子吸收極性的分子吸收了與其了與其振振動能階動能階對應的紅外線就會發生振動對應的紅外線就會發生振動

若分子本身沒有極性若分子本身沒有極性((偶極矩偶極矩)) 那就無法產生紅外那就無法產生紅外線線

產生紅外吸收的分子稱為紅外活性分子(IR-active)如COCO22分子分子反之為非紅外活性分子(IR-inactive)如OO22分子分子

A polar bond is usually IR-active

A nonpolar bond in a symmetrical molecule will absorb weakly or not at all (IR-inactive)

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

2

紅外線光譜

二紅外線光譜的三要素

一紅外線光譜的基本概念

三紅外線光譜的應用

五傅立葉轉換紅外線光譜儀

四樣品製備技術

3

4

基本原理

紅外線吸收光譜法與紫外線可見光吸收光譜法都屬於分子吸收光譜分子吸收光譜的範疇但光譜產生的原理不同紅外線吸收光譜是振動紅外線吸收光譜是振動--轉動光譜轉動光譜而紫外線可見光吸收光譜是電子光譜電子光譜因此紅外線的光譜和分子的振動轉動分子的振動轉動有密切關係

紅外線光區的波長範圍從 078-1000μm(780-1000000 nm)其波數從 12800~10 cm-1從儀器的應用範圍一般將紅外線光區分為三個區近紅外光區中紅外光區及遠紅外光區近紅外光區中紅外光區及遠紅外光區其波長波數及頻率範圍如表8-1所示IR儀器主要使用中紅外光區中紅外光區

5

一紅外線光譜的基本概念

帶有極性帶有極性((偶極矩偶極矩))的分子發生的分子發生振動（振動（vibrationvibration））就會就會產生產生紅外線紅外線反之帶有反之帶有極性的分子吸收極性的分子吸收了與其了與其振振動能階動能階對應的紅外線就會發生振動對應的紅外線就會發生振動

若分子本身沒有極性若分子本身沒有極性((偶極矩偶極矩)) 那就無法產生紅外那就無法產生紅外線線

產生紅外吸收的分子稱為紅外活性分子(IR-active)如COCO22分子分子反之為非紅外活性分子(IR-inactive)如OO22分子分子

A polar bond is usually IR-active

A nonpolar bond in a symmetrical molecule will absorb weakly or not at all (IR-inactive)

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

3

4

基本原理

紅外線吸收光譜法與紫外線可見光吸收光譜法都屬於分子吸收光譜分子吸收光譜的範疇但光譜產生的原理不同紅外線吸收光譜是振動紅外線吸收光譜是振動--轉動光譜轉動光譜而紫外線可見光吸收光譜是電子光譜電子光譜因此紅外線的光譜和分子的振動轉動分子的振動轉動有密切關係

紅外線光區的波長範圍從 078-1000μm(780-1000000 nm)其波數從 12800~10 cm-1從儀器的應用範圍一般將紅外線光區分為三個區近紅外光區中紅外光區及遠紅外光區近紅外光區中紅外光區及遠紅外光區其波長波數及頻率範圍如表8-1所示IR儀器主要使用中紅外光區中紅外光區

5

一紅外線光譜的基本概念

帶有極性帶有極性((偶極矩偶極矩))的分子發生的分子發生振動（振動（vibrationvibration））就會就會產生產生紅外線紅外線反之帶有反之帶有極性的分子吸收極性的分子吸收了與其了與其振振動能階動能階對應的紅外線就會發生振動對應的紅外線就會發生振動

若分子本身沒有極性若分子本身沒有極性((偶極矩偶極矩)) 那就無法產生紅外那就無法產生紅外線線

產生紅外吸收的分子稱為紅外活性分子(IR-active)如COCO22分子分子反之為非紅外活性分子(IR-inactive)如OO22分子分子

A polar bond is usually IR-active

A nonpolar bond in a symmetrical molecule will absorb weakly or not at all (IR-inactive)

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

4

基本原理

紅外線吸收光譜法與紫外線可見光吸收光譜法都屬於分子吸收光譜分子吸收光譜的範疇但光譜產生的原理不同紅外線吸收光譜是振動紅外線吸收光譜是振動--轉動光譜轉動光譜而紫外線可見光吸收光譜是電子光譜電子光譜因此紅外線的光譜和分子的振動轉動分子的振動轉動有密切關係

紅外線光區的波長範圍從 078-1000μm(780-1000000 nm)其波數從 12800~10 cm-1從儀器的應用範圍一般將紅外線光區分為三個區近紅外光區中紅外光區及遠紅外光區近紅外光區中紅外光區及遠紅外光區其波長波數及頻率範圍如表8-1所示IR儀器主要使用中紅外光區中紅外光區

5

一紅外線光譜的基本概念

帶有極性帶有極性((偶極矩偶極矩))的分子發生的分子發生振動（振動（vibrationvibration））就會就會產生產生紅外線紅外線反之帶有反之帶有極性的分子吸收極性的分子吸收了與其了與其振振動能階動能階對應的紅外線就會發生振動對應的紅外線就會發生振動

若分子本身沒有極性若分子本身沒有極性((偶極矩偶極矩)) 那就無法產生紅外那就無法產生紅外線線

產生紅外吸收的分子稱為紅外活性分子(IR-active)如COCO22分子分子反之為非紅外活性分子(IR-inactive)如OO22分子分子

A polar bond is usually IR-active

A nonpolar bond in a symmetrical molecule will absorb weakly or not at all (IR-inactive)

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

5

一紅外線光譜的基本概念

帶有極性帶有極性((偶極矩偶極矩))的分子發生的分子發生振動（振動（vibrationvibration））就會就會產生產生紅外線紅外線反之帶有反之帶有極性的分子吸收極性的分子吸收了與其了與其振振動能階動能階對應的紅外線就會發生振動對應的紅外線就會發生振動

若分子本身沒有極性若分子本身沒有極性((偶極矩偶極矩)) 那就無法產生紅外那就無法產生紅外線線

產生紅外吸收的分子稱為紅外活性分子(IR-active)如COCO22分子分子反之為非紅外活性分子(IR-inactive)如OO22分子分子

A polar bond is usually IR-active

A nonpolar bond in a symmetrical molecule will absorb weakly or not at all (IR-inactive)

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

Infrared Spectroscopy (IR)

Infrared RadiationThat part of the electromagnetic spectrum between the visible and microwave regions

08 μm (12500 cm-1) to 50 μm (200 cm-1)Area of Interest in Infrared Spectroscopy

The Vibrational portion of infrared spectrum

25 μm (4000 cm-1) to 25 μm (400 cm-1)

Radiation in the Vibrational Infrared region is expressed in units called wave numbers ( )(波數)Wave numbers are expressed in units of reciprocal centimeters (cm-1) ie the reciprocal of the wavelength (λ) expressed in centimeters

(cm-1) = 1 λ (cm)

ν⎯

ν⎯

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

7

Infrared Spectroscopybull The frequency of IR radiation is commonly

expressed in wave numbersbullbull Wave numberWave number the number of waves per

centimeter cm-1 (read reciprocal centimeters)bull the vibrational IR extends from 4000 cm-1 to 400

cm -1

(ν)-

ν = = 400 cm -110-2 m m　 -1

25 x 10 -5 m

= 4000 cm -1ν = 10-2 m m　 -1

25 x 10 -6 m

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

8

4000 400

25 20

0

100 Micrometers

Wavenumber (cm -1)Tra

nsm

ittan

ce (

)

波數

波長

透光百分率

IR Spectrum

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

9

IR Spectrum

bull No two molecules will give exactly the same IR spectrum (except enantiomers鏡面異構物)

bullbull Simple stretching(Simple stretching(簡易伸縮簡易伸縮) 1600) 1600--3500 cm3500 cm--11

bullbull Complex vibrationsComplex vibrations複雜振動複雜振動 600600--1400 cm1400 cm--11 called called the the ldquoldquofingerprint regionfingerprint region指印或指紋區指印或指紋區rdquordquo

Baseline

AbsorbancePeak

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

10

根據實驗技術和應用的不同將紅外光區分成三個區近紅外區中紅外區遠紅外區其中中紅外區是研究和應用最多的區域一般說的紅外光譜就是指中紅外區的紅外光譜一般說的紅外光譜就是指中紅外區的紅外光譜

紅外線區域的劃分

區功能變數名稱稱 波長(μm) 波數(cm-1) 能級躍遷類型

近紅外區 泛頻區 075-25 13158-4000 OHNHCH鍵的倍頻吸收

中紅外區 基本振動區 25-25 4000-400 分子振動伴隨轉動

遠紅外區 分子轉動區 25-300 400-10 分子轉動

波數)(

10)(4

1

mcm

μλν

minusminus =

紅外光區的劃分如下表

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

11

Infrared sub-regions Region Transition Wavelength

μm Wavenumber

cm-1

Near IR (NIR)

overtones 075-25 13300-4000

Mid IRFundamental

vibs rots 25-25 4000-400

Far IR skeletal rots

25-1000 400-10

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

12

分子振動方式

雙原子分子的振動形式可以用兩個小球的彈簧振動來模擬並以虎克定律來解說如下圖所示

δ δ

21

21

mmmm

+sdot

=μμπ

ν Kc2

1~ =

該系統的基本振動頻率的計算公式為

雙原子分子振動示意圖

由上式可見影響基本振動頻率的直接因素是相對原子質量和化學鍵結的力常數

其中

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

13

分子振動方式

原子沿鍵軸方向伸縮鍵長發生變化而鍵角不變的振動稱為伸縮振動它又分為對稱伸縮振動(νs ）和不對稱伸縮振動(νas ）

a伸縮振動(Stretchingνs and νas ）

一般將振動形式分成兩類伸縮振動和彎曲振動

Stretching Vibrations

symmetric anti-symmetric

Changes in bond lengthSymmetric Antisymmetric

伸展(Stretching) -兩原子之間的距離增加或是縮減

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

14

分子振動方式b彎曲振動（Bending用符號δ表示）

基團鍵角發生週期變化而鍵長不變的振動稱為彎曲振動彎曲

振動依彎曲平面的不同可分為

面內（in-plane）彎曲振動

rocking rocking 搖擺搖擺 and scissoring scissoring 剪動剪動

面外（out-of-plane）彎曲振動

Twisting Twisting 扭動扭動 and wagging wagging 搖動搖動

+ ndash + +

ndashscissoring twisting wagging

In-Plane Out-of-Plane

Changes in bond angle

彎曲-分子鍵角的改變搖擺

Bending Vibrations

rocking剪動剪動

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

15

In planeIn plane

Out of planeOut of plane

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

16

Sample Infrared Bending Mode The movement represented by this movie clip is the

symmetric O-H stretch in water In this mode the two bonds vibrate in a coupled manner such that both shorten lengthen together The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the asymmetric O-H stretch in water In this mode the two bonds vibrate in a coupled yet opposite manner ie one shortens while the second coupled vibration lengthens The movements shown here are exaggerated for clarity

The movement represented by this movie clip is the symmetric O-H bend in water In this mode the two bonds bend up and down in a coupled manner The movements shown here are exaggerated for clarity

Copyright 1998 BrooksCole Publishing Company

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

17

Normal modes ammonia (NH3)

ν2 = 950 cm-1

symmetric bendν4a = 1627 cm-1

asymmetric bendν4b = 1627 cm-1

asymmetric bend

ν1 = 3336 cm-1

symmetric stretch ν3a = 3414 cm-1

asymmetric stretch

ν3b = 3414 cm-1

asymmetric stretch

WEBhttpclasswebgmuedusdavischem332ammoniahtm

Note that n3a and n3b are degenerate modes as are n4a and n4bAll six normal modes will be IR active

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

18

二判讀紅外線光譜的三要素

1峰位（吸收尖峰波長位置）

2 峰強（吸收尖峰的大小）

3 峰形（吸收尖峰的形狀）3500 3000 2500 2000 1500 1000 500

20

40

60

80

100

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

19

二判讀紅外光譜的三要素

1峰位

分子內各種官能團的特徵吸收峰只出現在紅外光波譜的一定範圍如C=O的伸縮振動一般在1700 cm-1左右

紅外吸收峰的強度取決於分子振動時偶極矩的變化振動時分子偶極矩的變化越小譜帶強度也就越弱

一般說來極性較強的基團(如C=OC-X)振動吸收強度較大極性較弱的基團(如C=CN-C等)振動吸收強度較弱紅外吸收強度分別用很強(vs)強(s)中(m)弱(w)表示

2峰強

3峰形

不同基團的某一種振動形式可能會在同一頻率範圍內都有紅外吸收如-OH-NH的伸縮振動峰都在3400-3200 cm-1但二者峰形狀有顯著不同此時峰形的不同有助於官能團的鑒別

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

20

1 依虎克定律的解說可瞭解兩個物質間的振動頻率與兩個物

質的質量及兩個物質間的作用力有關一般而言質量越大

振動越慢作用力越大振動越快但不管如何振動越快就代

表所需的能量越高

2 將依虎克定律用在分子模型時也可用來解釋分子鍵結間振

動的模式兩個原子鍵結的振動頻率與兩個原子的質量及兩

個原子間的鍵結力量有關一般而言原子的質量越大振動

越慢但鍵結力越大則振動越快而振動越快就代表所吸收

或發射的波長越短

3 依原子質量而言振動頻率 C-H gt C-N gt C-O gt C-Br4 依鍵結力量而言振動頻率 C≣H gt C=H gt C-H5 依振動的方式而言振動頻率為 伸縮振動 gt 彎曲振動

分子鍵結與紅外線吸收之關係

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

21

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

22

1050-1250 strongweak1600-1680

1630-1800 strong2850-3100 medium to strong

strong and broad3200-3500medium3100-3500

IntensityFrequency (cm-1)Bond

C- HN- HO- H

C= OC= CC- O

1 O-H gt N-H gt C-H

2 C=O gt C-O

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

23

Summary of IR Absorptions

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

24

三紅外光譜的應用

紅外光譜的最大特點是具有特徵性譜圖上的每個吸收峰代表了分子中某個基團的特定振動形式據此進行化合物的定性分析和定量分析廣泛應用於石油化工生物醫藥環境監測等方面

（1）已知物的鑒定 在得到試樣的紅外譜圖後與純物質的譜圖進行比較如果譜圖中峰位峰形和峰的相對強度都一致即可認為是同一物質

1 定性分析

（2）未知物的鑒定是紅外光譜法定性分析的一個重要用途涉及到圖譜的解析

首先應瞭解樣品的來源用途製備方法分離方法理化性質元素組成及其它光譜分析資料如UVNMRMS等有助於對樣品結構資訊的歸屬和辨認

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

25

四紅外光譜的應用

下面列舉兩例加以說明

例一化合物C8H8O2的紅外光譜如右圖所示試推測其結構

解計算不飽和度

581 280 =++=Ω minus

21 13

4nnn minus

++=Ω

sim3000 cm-1有吸收說明有 和==C-H基團存在靠近1700 cm-1的強度吸收表明有C=O基團結合2730 cm-1特徵峰進一步說明有醛基 存在16001520 cm-1有吸收說明有苯環存在根據820 cm-1吸收帶苯為對位取代14601390 cm-1是－CH3特徵吸收峰根據以上解析並對照標準譜圖確定化合物為茴香醛

υC=O

-CH

-CH3

Ar-H

C=C -CH3γCH苯

C H

CHOH3CO

C H

O

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

26

四紅外光譜的應用

例二下列反應可能生成(A)和(B)兩個異構體用1H-NMR分析化學位移都一樣質譜MS分子離子峰也一樣用紅外光譜觀測時在1775 cm-1附近只看到一個吸收峰由此確定反應生成物為B若為Ａ屬酸酐類化合物C=O應有兩個吸收峰

(Ａ) (B)

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

27

三紅外光譜的應用

定量依據是Lambert-Beer定律定量時吸光度的測定常用基線法如圖所示圖中I與I0之比就是透射比

２ 定量分析

基線的畫法

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

28

四樣品製備技術

1 對試樣的要求

(1) 試樣應該是單一組分的純物質純度應gt98便於

與純化合物的標準進行對照多組分試樣應在測定前儘

量預先用分餾萃取重結晶區域熔融或色譜法進行

分離提純

(2) 試樣中不應含有游離水水本身有紅外吸收會嚴重

干擾樣品譜而且還會侵蝕吸收池的鹽窗

(3) 試樣的濃度和測試厚度應選擇適當以使光譜圖中的

大多數吸收峰的透射度處於15~70範圍內

(4)直接測定固體樣品時要求樣品顆粒直徑小於紅外線之波長否則會發生對入射光明顯的散射

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

29

四樣品製備技術

(1) 固體樣品的製備

a壓片法

將1~2mg固體試樣與200mg純KBr研細混合研磨到粒度小於

2μm在油壓機上壓成透明薄片即可用於測定

b糊狀法

研細的固體粉末和石蠟油調成糊狀塗在兩片空白之氯化鈉

窗片上進行測試此法可消除水峰的干擾液體石蠟本身

有紅外吸收此法不能用來研究飽和烷烴的紅外吸收

2樣品的製備

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

30

四樣品製備技術

薄膜法a 熔融法 對熔點低在熔融時不發生分解昇華和其他

化學變化的物質用熔融法製備可將樣品直接用紅外燈

或電吹風加熱熔融後塗製成膜

b 熱壓成膜法 對於某些聚合物可把它們放在兩塊具有拋

光面的金屬塊間加熱樣品熔融後立即用油壓機加壓冷

卻後揭下薄膜夾在夾具中直接測試

c 溶液制膜法 將試樣溶解在低沸點的易揮發溶劑中塗

在鹽片上待溶劑揮發後成膜來測定如果溶劑和樣品不

溶于水使它們在水面上成膜也是可行的比水重的溶劑

在汞表面成膜

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

31

四樣品製備技術

(2) 液體樣品的製備

a 液膜法對沸點較高的液體直接滴在兩塊鹽片之間形成

沒有氣泡的毛細厚度液膜然後用夾具固定放入儀器光路中

進行測試

b 液體吸收槽法對於低沸點液體樣品和定量分析要用固定

密封液體池制樣時液體池傾斜放置樣品從下口注入直至

液體被充滿為止用聚四氟乙烯塞子依次堵塞池的入口和出

口進行測試

(3) 氣態樣品的製備氣態樣品一般都灌注于氣體池內進行測

試

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

32

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

33

光源 Infrared Sources-1-能士特發光體

The Nernst Glower or Nernst Lamp An early light bulb which did not need to operate in vacuum like Edisonrsquos W filament bulb A ZrO2Y2O3Er2O3 (9073) mixed oxide A current passing through it would heat it to glowing Needed an external filament to get it hot to begin but then it could continue on its own

Gives a good spectrum from 1 to 10 microm intensity varies 3 orders of magnitude

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

34

Infrared Sources ndash 2-熾棒光源

The Globar is a competitor of the Nernst Glower Similar concept but uses SiC instead of metal oxides Can start heating from room temperature Globaris a bit better for wavelengths below 5 microm also the Globar requires water cooling of the filament supports

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

35

Infrared Sources ndash 3-白熱燈絲光源

Incandescent wire sources are longer lasting but lower intensity than the glower or globar A nichrome wire or rhodium wire heated to around 1100 K is a good IR source

A tungsten filament lamp can also work as a good source in the near-IR region 鎢 絲 燈 是 近 紅 外 線 光 區4000~12800 cm-1最常用的光源

為鎳鎔合金線圈

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

36

Infared Sources ndash 4-汞弧燈

The most difficult spectral region in which to function is the Far-IR Few sources are available The mercury arc lamp does provide some Far-IR radiation and has been used as a source for this type of experimentation

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

37

單色器使用稜鏡或光柵將複合光色散成單色波再射到偵測器上測量紅外線分光光度計的單色器最早用稜鏡目前普遍用光柵較易控制使用稜鏡時稜鏡的材料必須能透過紅外線且對光的色散儘可能大

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

38

Infrared Detectors 紅外線的偵測器

bull 紅外線的偵測器有三種型式(1）熱偵測器 (thermal detector) (2) 焦熱電偵測器(Pyroelectric detector） (3)光導偵測器(Photo-conducting detector)第一種用於光度計及分散式分光光度計第二及第三種用於較複雜的傅立葉轉換分光光度計

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

39

Infrared Detectors - 1熱偵測器熱偵測器係利用輻射的加熱效應用來偵測紅外線將輻射吸收而使溫度升高來測量輻射的量

A typical thermopile from Thermometrics

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

40

Infrared Detectors - 2熱偶計

bull熱偶計(thermo-couples)是將不同的兩金屬或兩半導體之兩端連接令其兩接點置於不同溫度中由其溫度差產生電位差其電位差與溫度差成正比

A bolometer from FIT Messtechnik Gmbh Germany

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

41

Infrared Detectors - 3焦熱電偵測器

bull由於焦熱電偵測器之感應時間很快能測知干涉儀的信號改變而適用於傅立葉轉換紅外線分光光度計

The PD-250 detector from Terahertz Technologies Made from LiTaO3

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

42

Infrared Detectors - 4光導偵測器

bull光導性物質吸收紅外線輻射光子會激發非光導性價電子至較高能階的傳導態而降低半導體的電阻測量電導或電阻的變化可偵測紅外線輻射的強度此偵測器主要適用於近紅外線光區

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

43

五Fourier轉換紅外光譜儀(FTIR儀)1 儀器組成及工作原理

傅立葉轉換紅外光譜儀 Fourier Transform InfraRedSpectrometer 主 要 由 光 源 ( 矽 碳 棒 高 壓 汞 燈 ) Michellson干涉儀檢測器電腦和記錄儀組成

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

44

FTIR與色散型紅外線分光光度計(IR)的主要區別是在干涉計及電子計算機二部分干涉計是使由光源發出的二光經過不同光程後再聚到某一點上時發生干涉現象如果將樣品放入光程中由於樣品吸收了某些頻率的能量使得干涉圖的強度發生變化它必須經過傅立葉轉換才能得到強度或透光率隨頻率或波數(或波長)變化的紅外線光譜圖此種變換十分複雜必須藉助計算機才能完成

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

45

五Fourier變換紅外光譜儀(FTIR儀)FI-IR光譜獲得過程如下圖所示意

背景干涉圖 樣品干涉圖

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

46

干涉儀之運動模式

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

47

Fourier Transform Infrared

httpwwwchemorsteduch361-464ch362irinstrshtm

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

48

五Fourier變換紅外光譜儀(FTIR儀)

3 儀器維護與簡單故障排除

2 優點

保持乾燥潔淨室溫維持18-25

(1)測量時間短(2)靈敏度高檢出限可達10-9~10-12 g(3)解析度高分辨本領高波數精度可達001cm-1(4)測定精度高重複性可達01(5)測定的光譜範圍寬由10000-l0 cm-1

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

49

六 FTIR結構外觀圖

Detector

Small cover

Large coverSource

Beamsplitter

(Rear)

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

50

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

51

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

52

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

53

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

54

Infrared Absorbances forCommon Functional Groups

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

55

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

56

Alkanes and alkenes

weak to medium1600 - 1680stretchingweak to medium3000 - 3100stretching

Alkene

AlkaneVibration

stretching

Hydro-carbon

Frequency(cm-1) Intensity

2850 - 3000 strongbending 1450 mediumbending 1375 and 1450 weak to medium

CH2

C-H

CH3

C=CC-H

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

57

Carbon-Carbon Bond Stretching

bull Stronger bonds absorb at higher frequenciesndash C-C 1200 cm-1

ndash C=C 1660 cm-1

ndash CequivC 2200 cm-1 (weak or absent if internal)

bull Conjugation lowers the frequencyndash isolated C=C 1640-1680 cm-1

ndash conjugated C=C 1620-1640 cm-1

ndash aromatic C=C approx 1600 cm-1

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

58

Carbon-Hydrogen Stretching

bull Bonds with more s character absorb at a higher frequencyndash sp3 C-H just below 3000 cm-1 (to the right)ndash sp2 C-H just above 3000 cm-1 (to the left)ndash sp C-H at 3300 cm-1

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

59

An Alkane IR Spectrum

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

60

An Alkene IR Spectrum

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

61

An Alkyne IR Spectrum

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

62

O-H and N-H Stretching

bull Both of these occur around 3300 cm-1 but they look differentndash Alcohol O-H broad with rounded tipndash Secondary amine (R2NH) broad with one

sharp spikendash Primary amine (RNH2) broad with two

sharp spikesndash No signal for a tertiary amine (R3N)

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

63

An Alcohol IR Spectrum

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

64

An Amine IR Spectrum

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

65

Carbonyl Stretching

bull The C=O bond of simple ketones aldehydes and carboxylic acids absorb around 1710 cm-1

bull Usually itrsquos the strongest IR signalbull Carboxylic acids will have O-H alsobull Aldehydes have two C-H signals around

2700 and 2800 cm-1

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

66

A Ketone IR Spectrum

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

67

An Aldehyde IR Spectrum

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

68

O-H Stretch of a Carboxylic Acid

This O-H absorbs broadly 2500-3500 cm-1 due to strong hydrogen bonding

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

69

Variations in C=O Absorption

bull Conjugation of C=O with C=C lowers the stretching frequency to ~1680 cm-1

bull The C=O group of an amide absorbs at an even lower frequency 1640-1680 cm-1

bull The C=O of an ester absorbs at a higher frequency ~1730-1740 cm-1

bull Carbonyl groups in small rings (5 Crsquos or less) absorb at an even higher frequency

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

70

An Amide IR Spectrum

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

71

Carbon - Nitrogen Stretching

bull C - N absorbs around 1200 cm-1

bull C = N absorbs around 1660 cm-1 and is much stronger than the C = C absorption in the same region

bull C equiv N absorbs strongly just above 2200 cm-1 The alkyne C equiv C signal is much weaker and is just below 2200 cm-1

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

72

A Nitrile IR Spectrum

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

73

bull Alcohols and ethers

bull Aromatic rings

Bond IntensityFrequency cm-1

medium1050 - 1250

medium broad3200 - 3500O-H (hydrogen bonded)C-O

Bond IntensityFrequency cm-1

strong to medium1475 and 1600medium to weak3030C- H

C= C

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

74

bull Amines

Bond Intensity

N-H

Frequency cm -1

3100-3500 medium to strong

Note 1amines show two bands in this region 2amines show only one band

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

75

bull Aldehydes and ketones

bull because few other bond vibrations absorb energy in this region a peak here is a reliable means of confirming the presence of a C=O group

bull the C=O group however may also be that of a carboxylic acid anhydride or ester

C=O IntensityFrequency cm -1

1705-1780 strongaldehyde amp ketone

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

76

bull Acids esters and amides

Additional Absorptions (cm-1)

O-H stretching at 2400-3400C-O stretching at 1210-1320

N-H stretching at 3200 and 3400(1amides have two N-H peaks)(2 amides have one N-H peak)

C-O stretching at 1000-1100and 1200-1250

Frequency(cm-1)Compound

1630-1680

1735-1800

1700-1725RCOH

RCOR

RCNH2

O

O

O

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

77

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Molecular Vibrations

1 Absorption of infrared radiation corresponds to energy changes on the order of 8-40 KJmole (2-10 Kcalmole

2 The frequencies in this energy range correspond to the stretching and bending frequencies of the covalent bonds with dipole moments

3 Stretching (requires more energy than bending)a Symmetrical 對稱

b Asymmetrical 不對稱

4 Bendinga Scissoring 剪動(in-plane bending)b Rocking 搖擺 (in-plane bending)c Wagging 搖動 (out-of-plane bending)d Twisting 扭動 (out of plane bending)

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

78

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)No two molecules of different structure will have exactly the same natural frequency of vibration each will have a unique infrared absorption pattern or spectrumTwo Uses1 IR can be used to distinguish one compound from another2 Absorption of IR energy by organic compounds will occur

in a manner characteristic of the types of bonds and atoms in the functional groups present in the compound thus infrared spectrum gives structural information about a molecule

The absorptions of each type of bond (NndashH CndashH OH CndashX C=O CndashO CndashC C=C CequivC CequivN etc) are regularly found only in certain small portions of the vibrational infraredregion greatly enhancing analysis possibilities

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

79

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)The Infrared Spectrum

A plot of absorption intensity ( Transmittance) on the y-axis vs frequency (wavenumbers) on the x-axis

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

80

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Principal Frequency Bands (from left to right in spectrum)

OminusH 3600 cm-1 (Acids - Very Broad Alcohols - Broad)NminusH 3300 - 3500 cm-1 (2 1 0 peaks ndash 1o 2o 3o)CequivN 2250 cm-1 (Nitrile)CequivC 2150 cm-1 (Acetylene)C=O 1685 - 1725 cm-1 (1715) (Carbonyl)C=C 1650 cm-1 (Alkene) 4 absorptions 1450-1600 (aromatic)CH2 1450 cm-1 (Methylene Group)CH3 1375 cm-1 (Methyl Group)CminusO 900 - 1100 cm-1 (Alcohol Acid Ester Ether Anhydride)

-CminusH (Saturated Alkane absorptions on Right side of 3000 cm-1)=C-H (Unsaturated Alkene absorptions on Left side of 3000 cm-1)=C-H (Aromatic absorptions) ndash Verify at 1667 ndash 2000 cm-1

equivC-H (Unsaturated Alkyne absorptions on Left side of 3000 cm-1)

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

81

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Suggested approach for analyzing IR Spectra

Step 1 ndash Check for the presence of the Carbonyl group (C=O) at 1715 cm-1 If molecule is conjugated the strong (C=O) absorption will be shifted to the right by ~30 cm-1ie ~1685 cm-1

If the Carbonyl absorption is present check forCarboxylic Acids - Check for OH group (broad absorption

near 3300-2500 cm-1)Amides - Check for NH group

(1 or 2 absorptions near 3500 cm-1) Esters - Check for 2 C-O group (medium

absorptions near 1300-1000 cm-1)Anhydrides - Check for 2 C=O absorptions near

1810 and 1760 cm-1

Aldehydes - Check for Aldehyde CH group (2 weak absorptions near 2850 and 2750 cm-1)

Ketones - Ketones (The above groups have been eliminated)

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

82

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 2 - If the Carbonyl Group is Absent Check for Alcohols Amines or Ethers

Alcohols amp Phenols - Check for OH group (Broad absorption near 3600-3300 cm-1

Confirm present of CminusO near1300-1000 cm-1

Amines - Check for NH stretch (Medium absorptions) near 3500 cm-1

Primary Amine - 2 PeaksSecondary Amine - 1 PeakTertiary Amine - No peaks

N-H Scissoring at 1560 - 1640 cm-1

N-H Bend at 800 cm-1

Ethers - Check for C-O group near 1300-1000 cm-1 and absence of OH

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

83

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)

Step 3 ndash Refine the Structure Possibilities by Looking for Double Bonds Triple Bonds and Nitro Groups

Double Bonds - Unsaturated C=C (and CequivC) stretch show absorptions on the left side of 3000 cm-1

Alkene C=C weak absorption near 1650 cm-1

Aromatic C=C (4 absorptions 1450-1650 cm-1)(Verify Aromatic at 1667 ndash 2000 cm-1)

Triple Bonds - R-C equiv N Nitrile - medium sharp absorption (stretch) near 2250 cm-1

R ndash C equiv C ndash R Alkyne - weak sharp absorption

(stretch near 2150 cm-1)R ndash C equiv C ndash H Terminal Acetylene

(stretch near 3300 cm-1)Nitro Groups - Two strong absorptions 1600 ndash 1500 cm-1

1

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

84

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Step 3 (Conrsquot)Aromatic Ring Absorptions

Aromatic unsaturated C=C bonds show an absorption on the left side of 3000 cm-1 but the aromaticity must be verified in the overtone region (1667 ndash 2000 cm-1) and the out-of-plane (OOP) region (900 - 690 cm-1)4 Medium to strong absorptions in region 1650 - 1450 cm-1

Many weak combination and overtone absorptions appear between 2000 and 1667 cm-1

The relative shapes and numbers (1 - 4) of the overtone absorptions can be used to tell whether the aromatic ring is monosubstituted or di- tri- tetra- penta- or hexa-substitutedPositional (ortho (o) meta (m) para (p)) isomers can also be distinguishedNote A strong carbonyl absorption can overlap these overtone bands making them unusable

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

85

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 3 (Conrsquot)

Aromatic Ring Absorptions (Conrsquot)The unsaturated =C-H ldquoOut-of-Plane (OOP) bending absorptions in the region 900 ndash 690 cm-1 can also be used to determine the type of ring substitutionThe number of absorptions and their relative positions are unique to each type of substitutionAlthough these absorptions are in the ldquoFingerprintrdquoregion they are particularly reliable for rings with Alkyl group substitutionsThey are less reliable for Polar substituents

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

86

Chem 315 Lab Experiment Overview Notes

Infrared Spectroscopy (IR)Step 4

If none of the above apply then the compound is most likely a

Hydrocarbonor

Alkyl Halide

Generally a very simple spectrum

Hydrocarbons - Check for saturated Alkane absorptions just on the right side of 3000 cm-1

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

87

Carbonyl (C=O) 1715-1685(Conjugation moves absorption to right ~30 cm-1

AcidEsterAmideAnhydrideAldehydeKetone

AlcoholAmineEther

Alkanes -C-HMethylene -CH2Methyl -CH3

Alkenes (Vinyl) -C=CAlkynes (Acetylenes) -CequivCAromatic (aryl) -C=C

Nitriles Nitro

Saturationlt 3000 cm-1

Yes No

Unsaturationgt 3000 cm-1

Hydrocarbons

Infrared Spectroscopy (IR)

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

88

Chem 315 Lab Experiment Overview Notes

Carbonyl (C=O) is Present

Acid - Broad OH Absorption 3300-2500 cm-1

Ester - C-O Absorption 1300-1000 cm-1

Amide - NH Absorption 3500 cm-1 (1 or 2 peaks)

Anhydride - 2 C=O Absorptions 1810 amp 1760 cm-1

Aldehyde - Aldehyde C-H Absorptions 2850 amp 2750 cm-1

Ketone - None of the above except C=O

Carbonyl is Absent

Alcohol - Broad OH absorption 3300 - 3000 cm-1

Also C-O absorption 1300 - 1000 cm-1

Amine - 1 to 2 equal NH absorptions 3500 cm-1

Ether - C-O absorption 1300 - 1000 cm-1

Infrared Spectroscopy (IR)

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

89

Chem 315 Lab Experiment Overview NotesInfrared Spectroscopy (IR)

Saturation

Unsaturation

Alkanes -C-H Stretch ndash several absorptions to ldquorightrdquo of 3000 cm-1

Methylene -CH2 1450 cm-1

Methyl -CH3 1375 cm-1

Double Bonds =C-H Stretch ndash several absorptions to ldquoleftrdquo of 3000 cm-1

OOP bending at 1000 ndash 650 cm-1

Alkenes (Vinyl) -C=C- Stretch (weak) 1675 ndash 1600 cm-1

Conjugation moves absorption to the rightAlkynes CequivC-H Terminal Acetylene Stretch at 3300 cm-1

Alkynes (Acetylenes) -CequivC Stretch 2150 cm-1

Conjugation moves absorption to the rightAromatic (aryl) =C-H Stretch absorptions also to left of 3000 cm-1

OOP bending at 900 ndash 690 cm-1

OOP absorption patterns allow determination of ring substitution (p 902 Pavia text)

-C=C 4 Sharp absorptions (2 pairs) 1600 amp 1450 cm-1

Overtone absorptions 2000 ndash 1667 cm-1

Relative shapes and numbers of peaks permit determination of ring substitution pattern (p 902 Pavia text)

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

90

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

CCmdashmdashH stretchingH stretching

bendingbending

bendingbending

bendingbending

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

91

Example of infrared spectrumExample of infrared spectrum

HexaneHexane

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

no peaks higher than 3000 cmno peaks higher than 3000 cm--11

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

92

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

peak higher than 3000 cmpeak higher than 3000 cm--11

C=CC=CmdashmdashHH C=CC=C

CHCH22=C=Cmdashmdash

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

93

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

spsp CCmdashmdashHH 33103310--33203320

spsp22 CCmdashmdashHH 30003000--31003100

spsp33 CCmdashmdashHH 28502850--29502950

spsp22 CCmdashmdashOO 12001200

spsp33 CCmdashmdashOO 10251025--12001200

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

94

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (multiple bonds)Stretching vibrations (multiple bonds)

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC CC 16201620--16801680

mdashmdashCC NN

mdashmdashCC CCmdashmdash 21002100--22002200

22402240--22802280

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

95

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (carbonyl groups)Stretching vibrations (carbonyl groups)

AldehydesAldehydes and and ketonesketones 17101710--17501750

Carboxylic acidsCarboxylic acids 17001700--17251725

Acid anhydridesAcid anhydrides 18001800--1850 and 17401850 and 1740--17901790

EstersEsters 17301730--17501750

AmidesAmides 16801680--17001700

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CC OO

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

96

Structural unitStructural unit Frequency cmFrequency cm--11

Bending vibrations of alkenesBending vibrations of alkenes

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

CHCH22RCHRCH

CHCH22RR22CC

CHRCHRciscis--RCHRCH

CHRCHRtranstrans--RCHRCH

CHRCHRRR22CC

910910--990990

890890

665665--730730

960960--980980

790790--840840

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

97

Infrared spectrum of 1Infrared spectrum of 1--hexenehexeneTransmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=C stretchC=C stretch

CHCH22=C=Cmdashmdashbendbend

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

98

Infrared spectrum of Infrared spectrum of terttert--butylbenzenebutylbenzene

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

ArArmdashmdashH stretch H stretch gt 3000gt 3000

monosubstitutedmonosubstitutedbenzenebenzene

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

99

Structural unitStructural unit Frequency cmFrequency cm--11

Stretching vibrations (single bonds)Stretching vibrations (single bonds)

OOmdashmdashH (alcohols)H (alcohols) 32003200--36003600

OOmdashmdashH (carboxylic acids) H (carboxylic acids) 30003000--31003100

NNmdashmdashHH 33503350--35003500

Table 134 (p 519)Infrared Absorption Frequencies

Table 134 (p 519)Table 134 (p 519)Infrared Absorption FrequenciesInfrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

100

Infrared spectrum of 2Infrared spectrum of 2--hexanolhexanol

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

OOmdashmdashH stretchH stretchCCmdashmdashH stretchH stretch

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies

101

Infrared spectrum of 2Infrared spectrum of 2--hexanonehexanone

Transmittance ()Transmittance ()100100

00

Wave number cmWave number cm--11

44004400 36003600 28002800 20002000 16001600 12001200 800800

C=O stretchC=O stretch

CCmdashmdashH stretchH stretch

• 紅 外 線 光 譜 法
• 紅外線光譜
• 基本原理
• 一紅外線光譜的基本概念
• Infrared Spectroscopy
• IR Spectrum
• IR Spectrum
• Infrared sub-regions
• Sample Infrared Bending Mode
• Normal modes ammonia (NH3)
• 二判讀紅外線光譜的三要素
• 二判讀紅外光譜的三要素
• Summary of IR Absorptions
• 三紅外光譜的應用
• ２ 定量分析
• 1 對試樣的要求
• 2樣品的製備
• 光源 Infrared Sources-1-能士特發光體
• Infrared Sources ndash 2-熾棒光源
• Infrared Sources ndash 3-白熱燈絲光源
• Infared Sources ndash 4-汞弧燈
• 單色器
• Infrared Detectors 紅外線的偵測器
• Infrared Detectors - 1熱偵測器
• Infrared Detectors - 2熱偶計
• Infrared Detectors - 3焦熱電偵測器
• Infrared Detectors - 4光導偵測器
• 五Fourier轉換紅外光譜儀(FTIR儀)
• 干涉儀之運動模式
• Fourier Transform Infrared
• 3 儀器維護與簡單故障排除
• Infrared Absorbances forCommon Functional Groups
• Carbon-Carbon Bond Stretching
• Carbon-Hydrogen Stretching
• An Alkane IR Spectrum
• An Alkene IR Spectrum
• An Alkyne IR Spectrum
• O-H and N-H Stretching
• An Alcohol IR Spectrum
• An Amine IR Spectrum
• Carbonyl Stretching
• A Ketone IR Spectrum
• An Aldehyde IR Spectrum
• O-H Stretch of a Carboxylic Acid
• Variations in C=O Absorption
• An Amide IR Spectrum
• Carbon - Nitrogen Stretching
• A Nitrile IR Spectrum
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies
• Table 134 (p 519)Infrared Absorption Frequencies