Alkenes and alkynes (II)

9.1 Introduction: Additions to alkenes

We shall study other examples of additions to the double bonds of alkenes. We begin with the additions of hydrogen halides, sulfuric

acid, water (in the presence of an acid catalyst), and halogens.

C C + A-B A C C BAddition

An Addition reaction

C C

H C C X

Alkene

H X

HOSO2OHH C C OSO2OH

H C C OH

HOH

Alkyl halide

Alkyl hydrogen sulfate

Alcohol

X C C X

X - X

Dihaloalkane

1. An addition reaction results in the conversion of one pi π -bond

and one sigma-bond into two sigma bonds

C C X C C YX - Y+

Bonds broken

2 - Bonds formed

sp2

sp3

Addition

2. The electrons of the pi-bond are exposed. Because the pi-

bond results from overlapping p orbital, the pi electrons lie above

and below the plane of the double bond:

C C

sp2

Electrophiles Ç×µçÊÔ¼Á

H+, X+,Lewis acids; BF3 and AlCl3Metal ions; Ag+, Hg2+, Pt2+,

Love elctrons

Hydrogen halides react with alkenes

H+ Cl-

Carbocation (Õý̼Àë×Ó£©

H + Cl- H Cl

Slow fast

C CC C

H

Cl

sp2

sp3

H+ Cl-H

+ Cl-

slow fast

Addition Reaction Mechanism

Carbocation (Õý̼Àë×Ó£©

9.2 Addition of Hydrogen Halides to Alkenes: Markovnikov’

s Rule ( 马氏规则）

What is it Mar’s Rule?-----The addition of HX to an alkenes, the hydrogen atom adds to the carbon atom of the double bond that already has the greater number of hydrogen atoms.

H2C CHCH3 + H+X- CH2CHCH3

H X

Markovnikov addition productCarbon atom with the greater number of hydrogen atoms

Markovnikov’s Rule ( 马氏规则）

H2C CCH3 + HCl CH2C(CH3)2

H Cl

(not ClCH2CH(CH3)2

CH3

tert-Butyl chloride2-Methylpropene

CH3

+ HCl

Cl

CH3

H

Methylcyclohexene 1-Chloro-1-Methylcyclohexane

A mechanism for addition of a hydrogen halide to an alkene

(two steps;)

Step 1 + HXSlow

H

+

rate-determining step

Step 2

H

+ + X-fast

H X

9.2A Theoretical explanation of Markovnikov’s Rule

CH

CH2 + H-Br CH3CHCH2H

Br

Markovnikov addition product

(not BrCH2CHCH3)H3C

H

Methyl push electron

1. Electronic Effects ( 电子效应）

H2C C + HCl CH2C(CH3)2

H Cl

(not ClCH2CH(CH3)2

CH3

tert-Butyl chloride2-Methylpropene

CH3

CH3

+ HCl

Cl

CH3

H

Methylcyclohexene 1-Chloro-1-Methylcyclohexane

2. The Stabilities of carbocation

（碳阳离子的稳定性解释马氏规则）

CH

CH2 + H-Cl

CH3CHCH2H

Markovnikov addition product

H3C

+b

a

CH3CHCH2

+

Cl-CH3CHClCH3

2o C+

Cl-CH3CH2CH2Cl

Anti-Mar's Rule1o C+

Stable

Unstable

2o C+ 1o C+

a

bH

The Stabilities of carbocation

C CH2+ H-Cl

CH3CCH2H

Markovnikov addition product

H3C

+b

a

CH3CCH2

+

Cl-CH3CClCH3

3o C+

Cl-CH3CHCH2Cl

Anti-Mar's Rule

1o C+

Stable

Unstable

3o C+ 1o C+

a

bH

CH3

CH3

CH3

CH3

CH3

Mar’s Rule help us to predict the outcome of the addition

reactionH2C C + HCl CH2C(CH3)2

H Cl

(not ClCH2CH(CH3)2

CH3

tert-Butyl chloride2-Methylpropene

CH3

Major Product

H2C C + I-Cl CH2C(CH3)2

I Cl

(not ClCH2CI(CH3)2

CH3

2-Chloro-1-iodo-2-methylpropane2-Methylpropene

CH3

(Major product)

9.2D An exception to Markovnikov’s Rule

( 马氏规则例外）The addition of HBr to alkenes, it is Only when HBr is used in the presence of peroxides (ROOR), it is an exception to Mar’ R

ule.

CH3CH=CH2 + HBr

ROORCH3CH2CH2Br

Major product

CH3CHBrCH3

Mar's product

Ionic reaction

Free radical reaction

9.3 Stereochemistry of the Ionic Addition to an alkene

CH3CH2CH=CH2 + HCl CH3CH2CHCH3*

Cl

(± )-2-Chlorobutane

We got a racemic form? Do you know why?

CH3CH2CH=CH2 + HCl CH3CH2CHCH3*

Cl

(± )-2-Chlorobutane

H+

CH2H

C+

H CH2CH3

Cl-H3C

Cl

H3CH2C

HCl-

CH3

ClH

CH2CH3

Achiral, trigonalPlanar carbocation( S )-2-Chlorobutane

(50%)( R )-2-Chlorobutane (50%)

Enantiomers

A recemic form (ÍâÏûÐýÌ壩

9.4 Addition of sulfuric acid to alkenes

+ HO S OH

O

O

C C

H

+

Step 1, The alkene accepts a proton (H+) from sulfuric acid to form a carbocation

CarbocationSulfuric acid

Slow

Alkene

C C

H

+

Carbocation

+ -O S OH

O

O

Hydrogen Sulfate ionÁòËáÇâ¸ù¸ºÀë×Ó

C C

H

OSO2OH

Alkyl hydrogen sulfateÍé»ùÇâÁòËáõ¥

fast

Step 2, The carbocation reacts with a hrdrogen sulfate ion to form an alkyl hydrogen sulfate

The addition of sulfuric acid is also regioselective ( 区域选择

性）

+ HO S OH

O

O

Sulfuric acidPropene

CH3CH=CH2

CH3CHCH2+

CH3CH2CH2+

Mar's addition

Anti Mar's addition

More Stablecarbocation

Less Stablecarbocation

HOSO2O-

CH3CHCH3

OSO2OH

Isopropyl hydrogen sulfate ÁòËáÇâÒì±ûõ¥

HOSO2O-

CH3CH2CH2OSO3H

Propyl hydrogen sulfate ÁòËáÇâÕý±ûõ¥

9.4A Alcohol from alkyl hydrogen sulfates

( 从硫酸氢乙酯制醇）Alkyl hydrogen sulfates can be easily

hydrolyzed to alcohols by heating them with water

+ HO S OH

O

O

Sulfuric acidPropene

CH3CH=CH2 CH3CHCH2+Mar's addition

More Stablecarbocation

HOSO2O-

CH3CHCH3

OSO2OH

Isopropyl hydrogen sulfate ÁòËáÇâÒì±ûõ¥H2O

Heat

CH3CHCH3

OH

+ H2SO4

Isopropanol

9.5 Addition of water to alkenes: Acid-catalyzed

hydrationThe acid-catalyzed addition of water to the double bond of an alkene is a method for the preparation of low molecular weight alc

oholsC C

Alkene

+

Water

C C

OH

H

Alcohol

HOHH+

Hydration (証죩

This reaction is followed Markovnikov's addition Rule

An example is the hydration of 2-methylpropene

C C

2-Methylpropene(Isobutylene)

+

Water

H3C C

CH3

C

H

OHH

H

tert-Butyl alcohol

H3C H

HH3C

HOHH+

Hydration (証죩

This reaction is also followed Markovnikov's addition Rule

Mechanism for the hydration of 2-methylpropene

C C

2-Methylpropene(Isobutylene)

+ H3C C

CH3

C

H

H

HH3C H

HH3C

HOHH+

Hydration (証죩 H

+

Step 1.

+ H2O

Carbocation

Slow

+

Step 2. H3C C

CH3

C

H

H

H

++ H2O:

Carbocation

H3C C

CH3

C

H

H

H

O+ H

H

fast

H3C C

CH3

C

H

H

H

O+ H

H

Step 3. +H2O:

fast

H3C C

CH3

CH3

O H

+ H3O+

tert-Butyl alcohol

Alkenes hydration is followed the occurrence of rearrangements

CH

CH2

3,3-Dimthyl-2-butene

+ H3C C

CH3

CHHOHH2SO4

Hydration (証죩 H

2o Carbocation

Slow

+C

CH3

CH3

H3C

CH3

+CH3

H3C C

CH3

C

3o Carbocation

CH3

CH3

+

H

H3C C

CH3

C CH3

CH3+

H

H2O:

OH2

-H+

H3C C

CH3

C CH3

CH3

H

OH

2,3-Dimethyl-2-butanol(Major product)

-CH3 immagration

9.6 Addition of bromine and chlorine to alkenes

1. Alkanes react with bromine

R H + Br2

Room temp

in the dark, CCl4

No appreciable reaction

Alkane

R H + Br2

Room temp

sunlight, CCl4Alkane

R Br + HBr

Alkyl halide Hydrogen bromide(detected by moist blue litmus)

(red brown)(Colorless)

2. Addition of bromine and chlorine to alkenes

+ Br2

Room temp

in the dark, CCl4

Alkene (red brown) Br Br

Vic-Dibromide(ÁÚ-¶þä廯Î (colorless)

Because of rapid decolorization of Br2/CCl4, it is a useful test for carbon-carbon multiple bonds (¼ìÑéÖؼü£©

Distinguish alkanes with alkenes （区别烷烃和烯烃）

+ Br2

Room temp

in the dark, CCl4

Alkene (red brown)

CH2=CH2 CH2BrCH2Br

1,2-Dibromoethane

(Colorless)

CH3CH3 Br2

Room temp

in the dark, CCl4

(red brown)

+ No reaction

Alkane

Distinguish cycloalkanes with cycloalkenes （区别环烷烃和环烯

烃）

+ Br2

in the dark, CCl4

cyclohexene (red brown)

Br2

Room temp

in the dark, CCl4

(red brown)

+ No reaction

trans-1,2-Dibromocyclohexane

cyclohexane

(Colorless)

Br

Br

H

H

3. Addition reaction of chlorine to alkenes

+ Cl2

2-butene2,3-Dichlorobutane

(Colorless)

CH3CH=CHCH3 CH3CHClCHClCH3-9oC

CH3CH2CH=CH2 + Cl2-9oC 1,2-Dichloropentane

(Colorless)

CH3CH2CHClCH2Cl

1-Pentene

9.6A Mechanism of halogen addition

Electrophiles Ç×µçÊÔ¼Á+ Br Br

Br+

Bromonium ion(äåÎÌÀë×Ó£©

Br-

Br+

Br

BrBr

Br

+

trans-Dibromide trans-Dibromide

9.7 Stereochemistry of the addition of halogens to alkenes

It is anti addition ( 反式加成）

Br2

CCl4

Br

H

H

Br

cyclopentene trans-1,2-Dibromocyclopentane(E)-1,2-Dibromocyclopentane

This anti addition of bromine to cyclopentene can be explai

ned by a mechanism

Br2

CCl4

cyclopentene

BrH H

+

Br-

Bromonium ion

BrH

BrH

HBr

HBr

+

Enantiomer

trans-1,2-Dibromocyclopentane(E)-1,2-Dibromocyclopentane

Cyclohexene

Br2

Br+

Br-

inversion

at C-1

Br

Br

+

Br

Br

Br

Br

Br

BrMost stableconformation

9.7A Stereospecific reactions （立体专一性反应）

trans-2-Butene

Bromonium ion

H

H3C H

CH3

+ Br2

H3C

HCH3

HBr+

Br-

ab

(chiral ÊÖÐÔ·Ö×Ó£©

Br

Br

H3C

H

H

CH3

Br

Br

H

H3C CH3

H

a

b

(2R, 3S) (meso ÄÚÏûÐý£©

(2R, 3S) (meso ÄÚÏûÐý£©

£¨¶Ô³ÆÖÐÐÄ£©

£¨¶Ô³ÆÖÐÐÄ£©

trans-2-Butene reacts with bromine

Cis-2-Butene reacts with bromine

cis-2-Butene

Bromonium ion

H3C

H H

CH3

+ Br2

H

H3CCH3

HBr+

Br-

ab

(achiral ·ÇÊÖÐÔ·Ö×Ó£©

Br

Br

H

H3C

H

CH3

a

b

(2R, 3R) ( chiral ÊÖÐÔ·Ö×Ó£©£¨ÎÞ¶Ô³ÆÖÐÐÄ£©

Br

Br

H3C

H CH3

H

£¨ÎÞ¶Ô³ÆÖÐÐÄ£©Enantiomer (¶ÔÓ³Òì¹¹Ì壩

(2S, 3S) ( chiral ÊÖÐÔ·Ö×Ó£©

9.8 Halohydrin formation （卤代醇的形成）

If the halogenation of an alkene is carried out in aqueous solution (rather than in carbon tetrachloride), the major product of the overall reaction is not a vic-dihalide, but rather it is a

halo alcohol called a halohydrin.

+ X2 + H2OC

X

C

OH

+ C

X

C

X

Halohydrin vic-Dihalide

Major product Minor product

Halohydrin formation can be explained by the following mechan

ism:

+ X H2OX

+Step1.C C

X+

Halonium ion

Step2. C C

X+

Halonium ion

H2O X-

Anti-addition

C

X

C

OH

+ C

X

C

X

Halohydrin vic-Dihalide

Major product Minor product

Isobutene reacts with bromine in water

C CH2

H3C

H3C

Br2

CH3

CH3C CH2

Br+

:OH2

H3C

CH3

+OH2

CH2Br

- H+

H3C

CH3

OH

CH2Br

(73%)

9.9 Radical addition to alkenes: The anti-Markovnikov addition o

f hydrogen bromideR O O R

An organic peroxideÓлú¹ýÑõ»¯Îï

R O O H

An organic hydroperoxideÓлú¹ý Ñõ»¯Çâ

HC CH2

HBrH3C H3C CHCH3

Br

No peroxideÎÞ¹ýÑõ»¯Îï

Markovnikov addition·ûºÏÂí¶û¿Æ·òÄá¿Æ·ò¼Ó³É

HC CH2

HBrH3C H3C CH2CH2

Br organic peroxide Óлú¹ýÑõ»¯Îï

Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³ÉR O O R

Do you know why?

HC CH2

HBrH3C H3C CH2CH2

Br organic peroxide Óлú¹ýÑõ»¯Îï

Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³ÉR O O R

Do you know why?

It is a free radical reaction (×ÔÓÉ»ù·´Ó¦£©

HC CH2

HBrH3C H3C CHCH3

Br

No peroxideÎÞ¹ýÑõ»¯Îï

Markovnikov addition·ûºÏÂí¶û¿Æ·òÄá¿Æ·ò¼Ó³É

It is an ionic reaction £¨ Àë×Ó·´ Ó¦£©

Free Radical reaction

R O O R

An organic peroxideÓлú¹ýÑõ»¯Îï

Step 1.heat

2 R O

Chain Initiation

Step 2. R O + HBr ROOH + Br

HC CH2Br

H3C

Chain Propagation

CH3CHCH2BrStep 3.

H3C CHCH2

Br

Anti-Markovnikov addition·´Âí¶û¿Æ·òÄá¿Æ·ò¼Ó³É

Step 4. CH3CHCH2Br H Br+

H

9.9A Other radical additions to alkenes

Tetrabromomethane (CBr4) reacts with 1-octene(1- 辛烯 )to yield 1,1,1,3-tetrabromonon

ane

CH3(CH2)5CH=CH2 + CBr3 CH3(CH2)5CHCH2CBr3

Br

1,1,1,3-tetrabromononane

(1,1,1,3-ËÄäåÐÁÍ飩

Br

Radical additions

ROOR

The mechanism for this reaction is as follows:

Chain Inition

Step 1 RO OR 2RO

RO + Br CBr3ROBr + CBr3Step 2

CH3(CH2)5CHCH2CBr3

Br

1,1,1,3-tetrabromononane

(1,1,1,3-ËÄäåÐÁÍ飩

Chain Propagation

Step 3 CH3(CH2)5CH=CH2 + CBr3 CH3(CH2)5CHCH2CBr3

Step 4 CH3(CH2)5CHCH2CBr3 Br CBr3+

Other examples of radical additions to alkenes are the

following:CH3(CH2)3CH=CH2 + HCCl3

ROOR

peroxideCH3CH2CH2CH2CH2CCl3

1,1,1-Trichlorohexane1-Hexene

(CH3)2C=CH2 + CH3CH2SHROOR

peroxide(CH3)2CHCH2SCH2CH3

Isobutene

CH3CH2C=CH2

CH3

+ CCl4 CH3CH2CCH2CCl3

CH3

Cl

1,1,1,3-Tetrachloro-3-methylpentane

peroxide

ROOR

Isopentene

9.10 Radical polymerization of alkenes ( 烯烃的自由基聚

合） :Addition polymers ( 加成聚合）

m CH2=CH2

EthyleneMonomer (µ¥Ì壩

Polymerization

ROOR* CH2CH2 *

n

Polyethylene (¾ÛÒÒÏ©£©polymer (¸ß·Ö×Ó»ò¾ÛºÏÎ

£¨m and n are large numbers)

m CH2=CH

Styrene (±½ÒÒÏ©£©Monomer (µ¥Ì壩

Polymerization

ROOR* CH2CH *

n

Polystyrene (¾Û±½ÒÒÏ©£©polymer (¸ß·Ö×Ó»ò¾ÛºÏÎ

£¨m and n are large numbers)

Other common addition polymers

m CH2=CH

Chloroethene (ÂÈÒÒÏ©£© (µ¥Ì壩

Polymerization

ROOR* CH2CH *

n

Poly(vinyl chloride) (¾ÛÂÈÒÒÏ©£©

Cl Cl

m CH2=CH

Acrylonitrile (±ûÏ©ë棩 (µ¥Ì壩

Polymerization

ROOR* CH2CH *

n

Polyacrylonitrile (¾Û±ûÏ©ë棩 Orlon °ÂÂÚ

CN CN

m CF2=CF2

Tetrafluoroethene (ËÄ·úÒÒÏ©£© (µ¥Ì壩

Polymerization

ROOR* CF2CF2 *

n

Polytetrafluoroethene (¾ÛËÄ·úÒÒÏ©£© £¨ËÜÁÏÍõ£©(Teflon)

m CH2=CCOOCH3

Methyl methacrylate (¼×»ù±ûÏ©Ëá¼×õ¥£© (µ¥Ì壩

Polymerization

ROOR* CH2C *

n

Poly(methyl methacrylate) (¾Û¼×»ù±ûÏ©Ëá¼×õ¥£© £¨Óлú²£Á§£©

CH3 CH3

COOCH3

9.11 Oxidations of alkenes ( 烯烃的氧化） : Syn hydroxyl

ation （顺式 - 羟基化作用）Alkenes undergo a number of reactions in which the carbon-carbon double bond is oxidized. Potassium permanganate (KMnO4) or osmiun tetroxide （ OsO4), for example, can be used to oxidize alkenes to 1,2-diols

(1,2- 二醇） called glycols （乙二醇） .C C

cold 5% KMnO4

or OsO4, Na2SO3OH OH

Syn-1,2-diols

C C

H

H

H

H

cold 5% KMnO4

or OsO4, Na2SO3

H

H

H

H

OH OH

1,2-Ethanediol(ethylene glycol)

Ethene

C C

H

H

H

H3C

cold 5% KMnO4

or OsO4, Na2SO3

H

H

H

H

OH OH

1,2-Propanediol(1,2-±û¶þ́ ¼£©(propylene glycol)

Propene

9.11A Syn hydroxylation of alkenes----Mechanism

C C

cold 5% KMnO4

O O

Mn

O O-

NaOH, H2O

Mn

O

O O

O-

Syn-1,2-diols

OH OH

OH-

H2O

C COsO4, Na2SO3

O O

Syn-1,2-diols

OH OH

Os

O O-

OH-

H2O

Os

O

O O

O

+ MnO4-

O

Mn

O

O O-

H H

H2O

OH-

OH OH

H H

cis-1,2-Cyclopentanediol(a meso compound)

Cold

+ OsO4

O

Os

O

O O

H H

NaHSO3

OH OH

H H

cis-1,2-Cyclopentanediol(a meso compound)

However, osmium tetroxide is highly toxic and is very expensive.

9.12 Oxidative cleavage of alkenes

Alkenes are oxidatively cleaved to salts of carboxylic acids by hot permanganate solu

tions.KMnO4

Acetic acid(ÒÒËᣩ

OH-, heatH3CHC CHCH3 2 CH3COOH

KMnO4

Acetic acid(ÒÒËᣩ

OH-, heatH3CC CHCH3 2 CH3COOH

CH3

CH3CCH3

O

+

acetone

CH3CH2C CH2

CH3

KMnO4

Carbon dioxide

OH-, heatCH3CH2CCH3

O

+

Butanone

O=C=O + H2O

An unknown alkene with the formula C7H12 undergoes oxidation by hot basic KMnO4 to yield, after acidifi

cation, only one product:

KMnO4, OH-, heat1,

2, H+C7H12 CH3CCH2CH2CH2CH2COOH

O

Unknown alkene(δ֪ϩÌþ)

CH3

1-Methylcyclohexene

9.12A Ozonolysis of alkenes ( 烯烃的臭 O3 氧化）

-O

O

O

O

O

O

Initial ozonideÒ»¼¶³ôÑõ»¯Îï

Second ozonide¶þ¼¶³ôÑõ»¯Îï

O

O O

Zn, H2OO O+

Aldehydes or ketones (È©»òͪ£©

reduction

The overall process of ozonolysis followed by reduction with zinc and water amounts to a disconnection of the carbon-carbon double bond

in the following fashion.

( 2 ) Zn, H2O reduction

R

R

R''

H

( 1 ) O3, CH2Cl2, -78oCR

R

O O

R''

H

+

Aldehydes (È©)

ketones (ͪ£©

( 2 ) Zn, H2O reduction

H3C

H3C

CH3

H

( 1 ) O3, CH2Cl2, -78oC

( 2 ) Zn, H2O reduction

CH

H

H

H

( 1 ) O3, CH2Cl2, -78oCH3C

CH3

H3C

H3C

O O

CH3

H

+

Acetaldehyde (ÒÒÈ©)

Acetone (±ûͪ£©

CH

H

O O

H

H

+

Formaldehyde (¼×È©)

Isobutylaldehyde (Ò춡ȩ£©

CH3

H3C

9.14 Addition of bromine and chlorine to alkynes

Br2, CCl4C C C C

Br

Br

Dibromoalkene

Br2, CCl4C C

Br

Br

Br

BrTetrabromoalkane

Cl2, CCl4C C C C

Cl

Cl

Dichloroalkene

Cl2, CCl4C C

Cl

Cl

Cl

ClTetrachloroalkane

It is usually possible to prepare a dihaloalkene by simply adding one molar equivalent of the halo

genBr2, (1 mol)

C C CH2OH C C

H3CH2CH2C

Br

Br

CH2OH

( 80%)

CH3CH2CH2

CCl4

HOOCC CCOOHBr2, (1mol)

C C

HOOC

Br

Br

COOH

( 70%)

CCl4Acetylenedicarboxylic acid(¶¡È²¶þËᣩ

trans or (E)-2,3-Dibromobutenedicarboxylic acid(2£¬3-¶þä嶡ϩ¶þËᣩ

9.15 Addition of hydrogen halides to alkynes ( 炔烃与卤化氢的

加成）C C C C

H

Cl

chloroalkene

HClHCl

follow Mar's RuleC C

H

H

Cl

Clgem-Dichloride

C C C C

H

Br

bromoalkene

HBrHBr

follow Mar's Rule

C C

H

H

Br

Brgem-Dibromide

C CHH3C C CH2

Cl

H3C

2-Chloropropene

HClHCl

follow Mar's Rule

H3C C C H

Cl

Cl

H

H

2,2-Dichloropropane

9.19 Simple chemical tests for alkanes, alkenes, alkynes, alkyl h

alides, and alcohols

9.19A Chemical tests

9.19B Concentrated sulfuric acid (H2SO4)

Alkenesalkynesalcohols H2SO4

AlkanesAlkyl halides

cold

Soluble in H2SO4

insoluble in H2SO4

9.19C Bromine in carbon tetrachloride ) (Br2/CCl4)

Alkenesalkynes

Br2 / CCl4

AlkanesAlkyl halidesalcohols

Decolorization of bromine

do not react with brominein the absence of light

9.19D Cold dilute potassium permanganate (KMnO4)

Alkenesalkynes

cold KMnO4

AlkanesAlkyl halidesalcohols

The deep-purple color of KMnO4 disappearto form MnO2

do not react with KMnO4

9.19E Alcoholic silver nitrate (AgNO3 / ROH)

AlkenesAlkynesAlcohols AgNO3Alkanes

ROHAlkyl halides

No reaction

AgX

9.19F Silver Nitrate in ammonia (AgNO3 / NH3)

AlkenesAlcohols

Ag(NH3)2+

Alkanes

OH-

Alkyl halides

AlkynesRC CH

No reaction

RC CAg

(terminal alkynes)

Special Topic C-----Divalent carbon compounds: Carbenes ( 卡宾 or

碳烯）

• Neutral divalent carbon compounds are called carbenes ( 卡宾 CH2: Methylene ）

• Most carbenes are highly unstable compounds.• The reactions show a stereospecificity• The reactions of carbenes are also of great sy

nthetic use

C.1 Structure of methylene (carbenes)

1. The preparation of carbenes

:CH2 N N:+

Heat

Light:CH2 :N N:+

DiazomethaneÖصª¼×Íé

Methyleneor carbene

Nitrogen

1.

2. H3C C

CH3

CH3

OKHCCl3 + (CH3)3COH + :CCl3-

:CCl2 + Cl-

+ K+

Dichlorocarbene¶þÂÈ¿¨±ö

potassium tert--butoxide

C.2 Reactions of Methylene

Methylene reacts with alkenes by adding to the double bond to form cyclopropa

nes:CH2

Methyleneor carbene

+

Dichlorocarbene¶þÂÈ¿¨±ö

R

H

H

R

+

R

H

H

R

:CCl2

Cl Cltrans-

trans-

:CCl2+

CHCl3 + (CH3)3COK

Cl

Cl

7,7-Dichlorobicyclo[4.1.0]heptane

12

3

4

56

7

Cyclohexene

Cyclohexene

+ CH2I2

Zn, Cu2Cl2

Bicyclo[4.1.0]heptane (92%)