有机化学 Organic Chemistry

第二章饱和烃：烷烃和环烷烃

Chapter2 Alkanes and Cycloalkanes

Chapter Two Saturated Hydrocarbons: Alkanes and Cycloalkanes

• What are Hydrocarbons?• Alkanes and Cycloalkanes.• General Formulas of Alkanes and Cycloalkanes.• Constitutional Isomers of Alkanes and Cycloalkanes.• Nomenclature of Alkanes and Cycloalkanes.• Structures of Alkanes and Cycloalkanes.• Physical Properties of Alkanes and Cycloalkanes.• Chemical Properties of Alkanes and Cycloalkanes.• Synthesis of Alkanes and Cycloalkanes.

What are Hydrocarbons?

• Hydrocarbons are compounds whose molecules contain only carbon and hydrogen atoms.

• 烃－－－由且只由碳和氢两种元素组成的有机化合物。

• 烃分子中的 H 原子被其它原子或基团取代后，可以生成一系列衍生物 derivative

Alkanes and Cycloalkanes

• Those hydrocarbons in which all of the carbon-carbon bonds are single bonds are called alkanes.（ Saturated Hydrocarbons)

• Cycloalkanes are alkanes in which all or some of the carbon atoms are arranged in ring.

• 烷烃－－－分子中的碳原子均以单键相连的烃。• 环烷烃－－－全部或部分碳原子成环状排列的烷烃。

2.1 General Formulas of Alkanes and Cycloalkanes

• Alkanes have the general formula CnH2n+2, where n is an integer ( 整数 ).

• Cycloalkanes have the general formula CnH

2n.

general formula ： CnH2n+2

甲烷Methane

丙烷Propane

丁烷Butane

乙烷Ethane

C

H

HH

H C

H

H C

H

HH

C

H

H

C

H

H

HC

H

H

H

C

H

H

C

H

H

HC

H

HH

C

H

H

H

2.2Constitutional Isomers of Alkanes and cycloalkanes

• Isomers are compounds that have the same numbers and kinds of atoms but differ in the way the atoms are arranged.

• Constitutional isomers are compounds that have their atoms connected in different orders.

• 同分异构体是具有相同的原子种类和个数而具有不同原子排列的化合物。

• 构造异构体是具有不同原子连接方式（原子种类和个数相同）的化合物。

Constitutional Isomers of Alkanes

• Constitutional isomers may have:

• different carbon skeletons,

• ( 不同的碳骨架）

• different functional groups,

• （不同的官能团）

• or different locations of a functional group along the chain.

• （官能团的位置不同）

CH3CHCH3

CH3

CH3CH2CH2CH3

CH3OCH3CH3CH2OH

CH3CHCH3

NH2CH3CH2CH2NH2

Constitutional and Stereo Isomers of Cycloalkanes

• How many constitutional isomers of C5H10 are there in cycloalkanes?

• Cis-Trans isomerism in cycloalkanes.

• （环烷烃的顺反立体异构现象）

环戊烷甲基环丁烷乙基 1,1- 二甲基 - 1,2- 二甲基 -

环丙烷环丙烷环丙烷

2.3Nomenclature of Alkanes and Cycloalkanes(1)

• Alkyl Group: If a hydrogen atom is removed from an alkane, the partial structure that remains is called an alkyl group.

Alkane Name Alkyl Group Name (abbreviation)

CH4

CH3CH3

CH3CH2CH3

CH3CH2CH2CH3 CH3CH2CH2CH2

CH3CH2CH2

CH3CH2

CH3Methane

Ethane

Propane

Butane

Methyl (Me)

Ethyl (Et)

Propyl (Pr)

Butyl (Bu)

Nomenclature of Alkanes and Cycloalkanes(2)

• Just as straight-carbon alkyl groups are generated by removing a hydrogen from an end carbon, branched alkyl groups are generated by removing a hydrogen atom from an internal carbon. For example:

CH3CH2CH3 CH3CH2CH2 CH3CHCH3

CH3CH2CH2CH3 CH3CH2CH2CH2 CH3CH2CHCH3

CH3CHCH3

CH3

CH3CHCH2

CH3CH3C

CH3

CH3

Propane （丙烷） Propyl （正丙基） Isopropyl （异丙基）

Butane （丁烷） Butyl （正丁基） sec-Butyl （仲丁基）

Isobutane （异丁烷） Isobutyl （异丁基） tert-Butyl （特丁基）


• Cycloalkyl Group: If a hydrogen atom is removed from an alkane, the partial structure that remains is called an cycloalkyl group. For example:

Cyclopropyl Cyclobutyl Cyclopentyl Cyclohexyl

环丙基环丁基环戊基环己基


• The degrees of alkyl substitution for carbon:

RCR

R

R

CR

R

R

HCR

H

H

H CR

R

H

H

Primary carbon is bonded to one o

ther carbon.

伯碳原子（一级碳原子）

Secondary carbon is bonded to two other carbons.

仲碳原子（二级碳原

子）

Tertiary carbon is bonded to three other carbons.

叔碳原子（三级碳原子）

Quaternary carbon is bonded to four other carbo

ns.

季碳原子（四级碳原子）

Nomenclature of Alkanes (1)

• The Unbranched Alkanes:• Name Number of Carbon Atoms Structure• Methane 1 CH4

• Ethane 2 CH3CH3

• Propane 3 CH3CH2CH3

• Butane 4 CH3CH2CH2CH3

• Pentane 5 CH3(CH2)3CH3

• Hexane 6 CH3(CH2)4CH3

• Heptane 7 CH3(CH2)5CH3

• Octane 8 CH3(CH2)6CH3

• Nonane 9 CH3(CH2)7CH3

• Decane 10 CH3(CH2)8CH3

• Undecane 11 CH3(CH2)9CH3

• Dodecane 12 CH3(CH2)10CH3

• Tridecane 13 CH3(CH2)11CH3

• Tetradecane 14 CH3(CH2)12CH3

• Pentadecane 15 CH3(CH2)13CH3


• 在中文中碳原子数目在十以内通常用传统的天干计数表示法，即：甲、乙、丙、丁、戊、己、庚、辛、壬、癸分别表示从一到十的碳数，十个碳原子以上分别用十一、十二、……数目表示。

• 烷烃的普通命名法：（正、异、新法）• “正”－无旁支直碳链；• “异”－“异头”接无旁支直碳链；• “新”－“新头”接无旁支直碳链。

CH3CHCH3

CH3CCH3

CH3

异头新头


• The International Union of Pure and Applied Chemistry

(IUPAC) system, in which a chemical name has three parts : prefix （前缀） , parent, （主体） and suffix （后缀） .

The parent selects a main part of the molecule and tells how many carbon atoms are in that part;

The suffix identifies the functional group family the molecule belongs to;

The prefix gives the locations of the functional groups and other substituents on the parent.

Prefix Parent Subffix

Where are the substituents? How manycarbons?

What family?


Most of complex branched-chain alkanes can be named by following four steps:

Step 1 Find the parent chain （选主链） .

Find the longest continuous chain of carbon atoms present in the molecule, if two different chains of equal length are present, choose the one with the larger number of branch points as the parent, and use the name of that chain as the parent name.

步骤一：选择连续的最长的取代基最多的碳链为主链，按主链的碳数定为“某烷”。（如果两条主链的长度一样，则选择旁支多的为主链。）


Step 2 Number the atoms in the parent chain （编序号） .

Beginning at the end nearer the first branch point, number

each carbon atom in the parent chain. If there is branching an

equal distance away from both ends of the parent chain, begin

numbering at the end nearer the second branch point.

步骤二：从靠近支链较近的一端为主链依次编号；如果两个支链靠近碳链的两端一样近，则应从较为靠近第二支链一端为主链编号（最低系列）。


Step 3 Identify and number the substituents （取代基编号） .

Assign ( 分配 ) a number to each substituent according to its point of attachment to the parent chain. If there are two substituents on the same carbon, give them both the same number. There must be as many numbers in the name as there are substituents( 取代基 ).

步骤三：按主链的编号顺序分别给出各取代基的编号，如果

同一个碳原子上有两个取代基，则给它们相同的编号。要做

到每个取代基都有一个编号。


Step 4 Write the name as a single word. （用一个词命名） .Use hyphens （短横） to separate the different prefixes, and use commas ( 逗号） to separate numbers. If two or more different substituents are present, cite them in alphabetical order. If two or more identical substituents are present, use one of the multiplier prefixes di-, tri-, tetra-, and so forth.

步骤四：用短横分割不同的取代基，用逗号分割数字编号；如果有不同的取代基出现，则以字母为序排列（中文以甲乙丙丁等为序）；相同的取代基用前缀 di-, tri-, tetra- 等修饰（中文用一、二、三、四表示），最终将化合物用一个完整

的词表示。

Nomenclature of Cycloalkanes (1)

A. Nomenclature of simple cycloalkanes. For example:

1-Ethyl-3-methylcyclohexane 3-cyclopropyl-2-methylhexane

(1 －甲基－ 3 －乙基环己烷）

但在中文中的命名稍有不同！


• B. Nomenclature of bicycloalkanes

• 双（桥）环烷烃的命名方法：• 从桥头碳开始先走大环经另一桥头碳再走小环为环上所有

碳原子编号，根据环中的碳数，定为“某烷”；• 旁支一律作为取代基，按“最低系列”使其编号最小；• 命名如下例：

1 2

345

6

7

8 2 ， 7 －二甲基－ 8 －乙基二环

[3 ， 2 ， 1] 辛烷


• C. Nomenclature of spiral cycloalkanes

• 螺环烷烃的命名方法：• 从与螺碳原子相连的小环碳原子开始先走小环经螺碳再走大

环为环中所有碳原子编号，根据环中碳数，定为“某烷”；• 旁支也作为取代基，同样按“最低系列”使其编号最小；• 命名如下例：

1 2

34

5

67

8

9 10 2 ， 6 ， 9 －三甲基螺 [4 ， 5]癸烷

2.4 Structures of Alkanes and Cycloalkanes (1)

A. Hybridization: sp3 Orbitals and the Structure of Alkanes

A theory was provided in 1931 by Linus Pauling, who showed mathematically how an s orbital and three p orbitals on an atom can combine, or hybridize, to form equivalent atomic orbitals with tetrahedral orientation.

甲烷的立体结构乙烷的立体结构

Structures of Alkanes and Cycloalkanes (2)

B. Structures of Cycloalkanes Assuming it’s symmetrical, cyclopropane must have C-C-C bond angles of 600. How can the hybrid-orbital model of bonding account for this large distortion of bonds angles from the normal 1090 tetrahedral value? The answer is the cyclopropane has bent bonds.

=>


C. Conformational Isomer （构象异构体） The different arrangements of atoms that result from rotation

about a single bond are called conformations, and a specific

conformation is called a conformer (conformational isomer).


D. Conformations of Ethane （乙烷的构象） Chemists represent conformational isomers in two ways,

Sawhorse representations and Newman projections.

（锯架式）（纽曼投影式）

H

H H

H

H

H

H

H H

H H

HH

H H

H H

H

H

H

HH H

H

Staggered （交叉式） Eclipsed （重叠式） Staggered ( 交叉式） Eclipsed （重叠式）

Sawhorse representationsSawhorse representations （（锯架式） Newman projectionsNewman projections （（纽曼投影式）


• Conformational Analysis of Ethane

=>


• E. Conformations of Butane （丁烷的构象）

CH3

H H

H

CH3

H

CH3

H H

H H

CH3

CH3

H H

H H

CH3H

CH3

H

CH3

HH

Staggered （交叉式） Eclipsed （重叠式） Staggered ( 交叉式） Eclipsed （重叠式） Sawhorse representationsSawhorse representations （（锯架式） Newman projectionsNewman projections （（纽曼投影式）


• Conformational Analysis of Butane


• F. Conformations of cyclohexane

a

a

a

a a

e

e

e

e

e

e1

23

45

6

a

1£¬3£¬5 ÔÚÍ¬ Ò»Æ½Ãæ P

2£¬4£¬6 ÔÚÍ¬Ò»Æ½Ãæ P'

2.5 Physical Properties of Alkanes and Cycloalkanes

• Boiling Points: The boiling points of the unbranched alkanes show a regular increase with increasing molecular weight.

• Melting Points: The unbranched alkanes do not show the same smooth increase in melting points with increasing molecular weight that they show in their boiling points.

• Density: As a class, the alkanes and cycloalkanes are the least dense of all groups of organic compounds.

• Solubility: Alkanes and cycloalkanes are almost totally in soluble in water because of their very low polarity and their inability to form hydrogen bonds.

• •

2.6Chemical Properties of Alkanes and Cycloalkanes (1)

Alkanes, as a class, are characterized by a general inertness（不活泼） to many chemical reagents. Carbon-carbon and carbon-hydrogen bonds are quite strong, they do not break unless alkanes are heated by to very high temperatures. The chemical reactivity of alkanes and cycloalkanes as following: A. The reactions of alkanes with Halogens (Free radical substitution) B. Oxidation of alkanes and cycloalkanes C. Isomeration of alkanes and cycloalkanes D. Addition of small cycloalkanes

Chemical Properties of Alkanes and Cycloalkanes (2)

A. The Reactions of Alkanes with Halogens---Free radical substitution. The reaction of an alkane with Cl2 occurs when a mixture of the two is irradiated with ultraviolet light. For example:

CH4 Cl2 CH3Cl HCl+hv

+

+

STEP 1

STEP 2

Cl Cl hv 2 Cl.Cl.+ CH4 ClH + CH3.

STEP 3 CH3.+ Cl2 Cl.CH3Cl +

CH3. Cl. CH3Cl

The mechanism of the reaction:

Chain Initiation

Chain Propagation

Chain Termination


• More examples:

CH3CH2CH3 +CH3CH2CH2Cl CH3CHCH3

Cl+ Cl2

hvRT

45% 55%

CH3CHCH3

CH3

+ Cl2hvRT CH3CHCH2Cl

CH3CH3CCH3

CH3

Cl+

64%64% 36%

CH3CHCH3

CH3

+ Br2hv

CH3CHCH2BrCH3

CH3CCH3

CH3

Br+heat

99%>TraceConclusion:

A. Reactivity of Hydrogen: Tertiary H> Secondary H>Primary H

B. Reactivity of Halogens: F2>Cl2>Br2>I2

C. Selectivity of Halogens: I>Br>Cl>F


• B. Oxidation of Alkanes and Cycloalkanes

• The reaction with oxygen occurs during combustion in an engine or furnace when the alkanes is used as fuel.

O2MnO2

107~110oC

CO2H

CO2H+

C.C. Isomeration of Alkanes and Cycloalkanes

CH2CH3 CH3CH3

CH3

CH3

CH3

+ 50oC

AlCl3 AlCl3

50oC

CH3CH2CH2CH3 CH3CHCH3

CH3AlCl3/HCl

1~2MPa95~150oC

CH4 + 2 890kJ/molO2 CO2 H2O+2 +


• D. Addition of small cycloalkanes

• Addition of Hydrogen (Reduction)

• Addition of Bromine

• Addition of Hydrogen Halide

•

• BACK

+ H2Ni

200 oC

80 oCCH3CH2CH3

+ H2Ni

CH3CH2CH2CH3

300 oC+ H2

NiCH3CH2CH2CH2CH3

+ Br2RT

BrCH2CH2CH2Br

+ Br2 BrCH2CH2CH2CH2Br

+ HBr

+ HBr

Br

Br

2.7 Synthesis of Alkanes and Cycloalkanes(1)

• Mixtures of alkanes as they are obtained from petroleum are suitable as fuels. However, in our laboratory work we often have the need for a pure sample of a particular alkane. Several such methods are available, and three are outlined here. In subsequent chapters we shall encounter others.

• A. Hydrogenation of Alkenes and Alkynes.

• B. Reduction of Alkyl Halides

• C. Corey-House Reaction

Synthesis of Alkanes and Cycloalkanes(2)

• A. Hydrogenation of Alkenes and Alkynes.

• Alkenes and alkynes react with hydrogen in the presence of metal catalysts such as nickel, palladium, and platinum to produce alkanes. For example:

• BACK

CH3CH=CH2 CH3CH2CH2Ni

50 atm

/C2H5OH

CO

25+ H H

CH3COOCH2CH3

Pd+ H H2


• B. Reduction of Alkyl Halides.• Most alkyl halides react with zinc and aqueous acid to pro

duce an alkane. For example:

• When heated dialkylhalides can react with zinc to produce cycloalkanes. For example:

• BACK

HBr

ZnCH3CH2CHCH3

BrCH3CH2CHCH3

H

BrBr Zn+ NaI/C2H5OH


• C. Corey-House Reaction• When the lithium dialkylcuprate is treat with alkyl halide,

coupling takes place between one alkly group of the lithium dialkylcuprate and the alkyl group of the alkyl halide.

• For example:

• BACK

Br CH3(CH3)2CuLi+ Et2O

+ CH3Cu + LiI

I CH3(CH3)2CuLi+ Et2O

+ CH3Cu + LiI

Specific words for you in this chapter(1)

• Hydrocarbon( 烃 ) Saturated Hydrocarbon( 饱和烃 ) molecule ( 分子 ) alkane ( 烷烃 )

• cycloalkane ( 环烷烃 ) Isomer ( 同分异构体 ) • Constitutional isomers ( 构造同分异构体 ) • carbon skeleton ( 碳骨架 ) Cis-Trans isomerism ( 顺反异

构 ) Alkyl Group ( 烷基 ) Primary ( 伯 ) • Secondary ( 仲 ) Tertiary ( 叔 ) Quaternary ( 季 )• substituent( 取代基 ) parent chain ( 主链 ) • hybridization （杂化） conformation （构象异构） co

nformer （构象异构体） stagger （交叉）• eclipse （重叠） boiling point （沸点）• melting point （熔点） density （密度）

Specific words for you in this chapter(2)

chemical reagent （化学试剂） reactivity （反应活性） halogen （卤素） substitution （取代反应）

oxidation （氧化反应） reduction （还原反应） isomeration （异构化反应） addition （加成反应） mixtur

e （混合物） irradiate （照射） mechanism （反应机理） synthesis （合成）alkyl halide （烷基卤化物） aqueous acid （酸的水溶液） catalyst （催化剂） lithium dialkylcuprate （二烷基铜锂）

Additional problems of this chapter

• 2.1 Draw a compound that:

• (a) Has only primary and tertiary carbons (b) Has no primary carbons

• (c) Has five secondary carbons (d) Has only primary and quaternary carbons

• 2.2 Draw and name as many compounds as you can that fit the following descriptions:

• (a) Alkanes with formula C7H16 (b) Cycloalkanes with formula C5H10

• 2.3 Sight along the C2-C3 bond of 2,3-dimethylbutane, and draw a Newman projection of the most stable conformation.

• 2.4 Draw the most stable chair conformation of the following molecules:

• (a) cis-1-Ethyl-2-methylcyclohexane (b) cis-1-tert-Butyl-4-ethylcyclohexane

• 2.5 Predict the major product(s) of the following reactions:• (a) (b)

• (c) (d)

Br2

hv ?Br2 ?CCl4

Zn?HBr

Br

+ (CH3)2CuLiEt2O ?

Br

Documents

有机化学 Organic Chemistry