Organic Chemistryfor Students of Medicine and Biology大学化学III和大学化学III（2）

March 4, 2015

Chapter 4 Alkanes Chapter 4 Alkanes and Cycloalkanesand Cycloalkanes

((烷烃和环烷烃烷烃和环烷烃))

Refining of petroleum, a majornatural source of alkanes

March 3, 2015

Homologous series and isomerism of alkanes

Homologous series is a family of compoundsin which each member differs from the next by one methylene (CH2) group.

CnH2n+2

IsomerismIsomers : compds that have the same molecular formula but different structural formula, therefore they have the different chemical and physical properties. ( different compds with identical molecular formula are isomers.)

4.1.1 Nomenclature of Alkanes

1. Common names (普通命名法)甲乙丙丁戊己庚辛壬癸

n-(正); Iso-(异); Neo-(新)2. Systematic Nomenclature (IUPAC

names)International Union of Pure and Applied Chemistry

Alkane Nomenclature# Carbons Name

12 3 4 5

methaneethanepropanebutanepentane

Alkane Nomenclature# Carbons Name

6 7 8

hexaneheptaneoctanenonanedecane

9 10

•How many butanes are there?

CnH2n+2

Methane CH4

Ethane CH3CH3

Propane CH3CH2CH3

Butanes

b.p -0.4o

b.p -10.2o

n-butane

isobutane

CH3CH2CH2CH3

CH3CHCH3

CH3

How many pentanes are there?

CH3CH2CH2CH2CH3

CH3CH2CHCH3

CH3

CH3CCH3

CH3

CH3

n-pentane

isopentane

neopentane

Pentanes

Molecular Formula Isomers

CH4

C2H6

C3H8

1

11

C4H10 2

C6H14

C10H22

C20H42

C40H82

5

75

366,31962,491,178,805.831

Alkyl GroupsAlkane Alkyl

CH4 CH3-methane methyl

CH3CHCl

CH3

CH3CH

CH3

CH3CH2CH2propyl

isopropyl

isopropyl chloride

CH3CH2CH2CH2

CH3CHCH2

CH3

CH3CHCH2CH3

CH3C

CH3

CH3

• n-butyl

• isobutyl

• s-butyl

• t-butyl

CH3C

CH3

CH3

OH

t-butyl alcohol

What is the common name of this compound?

CH2CHCH3

CH3Cl

isobutyl chloride

What is the common name of this compound?

Isopropyl alcohol

What is the common name of this compound?

CH3CHCH2CH3

OH

s-butyl alcohol

CH3CCH2

CH3

CH3

neopentyl

neopentyl alcohol(CH3)3CCH2OH

IUPAC Names1. Longest continuous chain as theparent chain.2. Position by number3. Number from end which gives

the smallest numbers4. Use di-, tri-, tetra-5. Arrange in alphabetical order

(except di-, tri-, tetra-, sec-, tert)

Common Name:isopentane

IUPAC Name:

2-methylbutane

CH3CHCH2CH3

CH3

2-methylpentane

(Bond line formula)

CH3CHCH2CH2CH3

CH3

IUPAC Name?

2,3-dimethylpentane

IUPAC Name?

2,3-dimethylpentane

IUPAC Name?

3-methylpentane

IUPAC Name?

3-methylpentane

CH3 CH2 CH CH CH2 CH CH2 CH3

CH3

CH3

CH2 CH3

1 2 3 4 5 6 7 8

6-Ethyl-3,4-dimethyloctane

4-ethyl-3,5-dimethyloctane

CH3 CH CH2 CH CH2 C CH3

CH3

CH

CH3

CH3

CH3

CH2

CH2 CH3

4-Isopropyl-2,6,6-trimethylnonane

methylcyclopropane

Cycloalkanes

ethylcyclopentane

cyclohexane

CH3

H

CH2CH3

IUPAC Name?

Methylcyclobutane

3-cyclopropylpentane

The types of carbon atomPrimary carbon ; Secondary carbon ; Tertiary

carbon; Quaternary carbon

OOO O4321

C

C C

C

C

C

CH C

C

CCH2

CCH3 C

2.1.2 Conformation of alkane

Different arrangements of atoms that result from rotation around a single bond are called conformations, and a specific conformation is called a conformatonal isomer (Conformer).

Conformations

CH3CH3

Ethane

C C

H

HHH

HH

Out

Back

In the plane

C - C

H

HH

HH

H

H

HHHH

H

H

HH

HH

H

Wedge

Sawhorse

Newman

Frontcarbon

Backcarbon

120o

Newman Projection Formula

Rotate about C-C Bond

Staggered Conformation

Eclipsed Conformation

Conformations of n-ButaneCH3CH2-CH2CH3

Rotate about this bond

GaucheAnti

(Most stable) (In between)

CH3

CH3H

H

H

H

CH3

CH3

H

H

H

H

Gauche Anti

ReviewNomenclature

Alkanes

Alkyl Groups

Common Names

IUPAC Names

Conformation

Conformational isomer

2.1.3 Chemical properties of alkanes

C--C, C—H bond energy; Bond polarity

CnH2n+2 + 3n+12 O2 nCO2 + (n+1)H2O + 热能

Halogenations of alkanes

are substitution reactions in which a halogen replaces one (or more) of the

alkane’s hydrogen atoms to give alkylhalides.

+ X2 C X + HXC H

CH3-H + Cl-Cl CH3-Cl + H-ClHow does this reaction take place?

1. Stepwise?

2. Concerted?

How Break Bonds?X : Y

1. Ionic: X+ :Y- heterolytic

2. Radical: X . .Y homolytic

CH4 + Cl2

CH3Cl + HCl

Energy

No reaction when methane and chlorine are mixed

Products

++

E N E R G Y

Reaction Coordinate

Reactants

Activation Energy

Transition State

Cl2

Cl2

Cl2

Cl2

Cl2 Cl2

Cl2

Cl2Cl2

Cl2

CH4

CH4

CH4

CH4

CH4

CH4

CH4

CH4

Light makes reaction start

Chlorine

Cl2

Cl2

Cl. .Cl

Cl2

Cl2

Cl2 Cl2

Cl2

Cl2Cl2

Cl2

CH4

CH4

CH4

CH4

CH4

CH4

CH4

CH4

Cl2 2 Cl.light

Cl2

.Cl

Cl2

Cl2

Cl2 Cl2

Cl2

Cl2Cl2

Cl2

CH4

CH4

CH4

CH4

CH4

CH3.

CH4

CH4

HCl

Cl. + CH4 HCl + CH3.

Transition State

Cl .......H ....CH3

. .δ δ

Cl

.Cl

Cl2

Cl2

Cl2 Cl2

Cl2

Cl2Cl2

Cl2

CH4

CH4

CH4

CH4

CH4

CH3

CH4

CH4

HClCl.

CH3. + Cl2 CH3Cl + Cl.

Initiation Step:

Propagation Steps:Determining-rate step

Chain-Terminating Steps

RegioselectivityCl2

light

28%

72%

CH3CH2CH2CH3

Cl2

light

primary radical secondary radical

CH3CH2CH2CH3

CH3CH2CH2CH3 CH3CH2CHCH3

CH3CH2CH3

CH3CH2CH2. + H.

CH3CHCH3 + H..

410 KJ/mol98 kcal/mol 397 KJ/mol

95 kcal/mol

Bond dissociation energy

CH3-C-CH2-H

H

CH3

H

CH3

CH3-C-CH2 .CH3

CH3-C-CH2-H .

H.

410 KJ/Mole 380 KJ/Mole

Relative Stability

R3C. R2CH. RCH2.> >

Relative Rate of Chlorination

R3CH5.2

R2CH2

3.9

RCH3

1.0

Cl2

light

What is the major product?

CH3CHCH3

CH3

Cl2

light

36% 64%

CH3CHCH3

CH3

CH3CHCH2Cl

CH3CH3CCH3

CH3

Cl

Br2

light

3% 97%

CH3CH2CH3

CH3CH2CH2Br CH3CHCH3

Br

CH3CH2CH2CH3

2%

98%

Br2

light

Relative Rate Bromination

R3CH > R2CH2 > RCH3

1640 82 1

More Reactive

Less Selective

The order of halogen reactivity

• F2 >Cl2>Br2>I2

How do you make:

t-butyl bromide

CH3CCH3

CH3

Br

Br2

lightCH3CHCH3

CH3CH3CCH3

CH3

Br

Cl

HCl2

Light

The stability of radicals The alkyl radical is sp2 hybridization.

the stability sequence of them is

3o >2o >1o > CH3·

Methyl radical

Trigonal planar

The p orbital contains the unpaired electron

Free radicals

Chinese book: P65

Summary

Free Radical reactionInitiationPropagationTermination

Relative Radical StabilityTertiary>Secondary>Primary

GJX-2015