Chapter 3 Alkenes

3.1 Alkene Nomenclature3.2 Structure of Alkenes3.3 Isomerism in Alkenes 3.3.1 Stereo-isomerism in Alkenes 3.3.2 Naming Stereoisomeric Alkenes 1. Naming by term Cis-trans 2. Naming by the E, Z Notational System 3.4 Reactions of Alkenes 3.4.1 Electrophilic Addition of Alkenes (1) Addition of Hydrogen Halides to Alkenes

Orientation of electrophilic addition Mechanism of the Reaction The stability of carbocations Carbocation Rearrangements Peroxide effect(2) Addition of Sulfuric acid to Alkenes(3) Acid-catalyzed Hydration of Alkenes(4) Hydroboration-Oxidation of alkenes(5) Addition of Halogen to Alkenes

(6) Conversion of Alkenes to Vicinal Halohydrin 3.4.2 Hydrogenation ofAlkenes Heat of hydrogenation Stabilities of alkenes Mechanism of alkenes hydrogenation Stereochemistry of Alkenes hydrogenation Heterogeneous reaction 3.4.3 Oxidation of Alkenes (1) Epoxidation of Alkenes (2) Hydroxylation of alkenes (3) Oxidative cleavage of alkenes: (A) Ozonolysis of Alkenes (B) With KMnO4 solution 3.4.4 Reaction of Alkenes with Alkenes: Polymerization

Alkenes: (Olefin) Hydrocarbon containing carbon-carbondouble bondThe site of reactions The functional group

（反应部位） （官能团）

Aliphatichydrocarbons

Saturated( 饱和烃 )

Unsaturated( 不饱和烃 )

Alkanescycloalkanes

AlkenesAlkynes

C CR

H

R'

R''P76P76

Isobutylene（异丁烯）

C CH2H3C

H3C

H

CH3

CH3CH3

α- Pinene（ α- 蒎烯）

Farnesene（法呢烯）

3.1 Nomenclature of Alkenes

Terpene（萜烯）

IUPAC Names:1. Give the base name by selecting the longest continuous carbon chain including the double bond .

-ene （某烯）-ene （某烯）

2. Number: Give the boubly bonded carbons the lower number.

3. The location of substituents like alkanes.

4. When C number is over 10: 称某碳烯CH3(CH2)3CH CH(CH2)4CH3

5-Undecene 5- 十一碳烯

C CCH3CH2

CH3CH2CH2

HH

2-Ethyl-1-pentene

CH3

CH3

4,4-Dimethylcycloheptene

Alkenyl groups （烯基） :Vinyl （乙烯基）Allyl (Allylic group)

（烯丙基）CH3 CH CH

CH2 CH

CH2 CH CH2

Propenyl （丙烯基）CH2 C

CH3

Isopropenyl （异丙烯基）

CH2Methenecyclohexane（亚甲基环己烷）

3.2 Structure of AlkenesStructure of Ethylene:sp2 Hybrid orbitals

P16, 1.9P16, 1.9

C:Ground state

2p

2s

1sPromotionof electronPromotionof electron

Exited state

2p

2s

1s

sp2-hybridized state

1s

2p

sp2

Hybri-dization

Hybri-dization

An sp2 orbital1/3 s orbital2/3 p orbital

Three equivalent sp2 hybrid orbitals lie in a plane at angle of 120°to one another.

Geometric structure of C atom with sp2-hybrid: Planar triangle( 平面三角 )

A single unhybridized p orbital perpendicular to the sp2 plane. In the molecule of Ethylene :

The formation of C _ Cσbond: sp2 _ sp2 overlap

The formation of C-C πbond: 2p-2p side by side overlap.

The formation of C-H σbond : sp2-1s overlap.

One C-C σbond and 4 C-H σbond are coplanar.

The formation of C-C πbond:2p-2p side by side overlap.

p orbital overlap

H

H

H

H

σ- bond

p orbitaloverlap

C C

σbond

πbondπbond

Carbon-carbon double bond

Models of Ethylene

3.3 Isomerism in Alkenes3.3.1 Stereo-isomerism in Alkenes P80, 3.3P80, 3.3

C CH

HH

CH2CH3C C

H

CH3H

CH3C C

H3C

HH

CH3C C

H3C H

H CH3

1-Butene2-Methyl-2-

butene Isobutene

cis-2-Butene trans-2-Butene

Constitutional isomers

Constitutional isomers

(I)

(III) (IV)(II)

(I) (II) (III) (IV)

StereoisomersStereoisomers(III)

(IV)Cis-trans isomers

The different spacialarrangement of atoms or atomic groups.

cis-2-Butene

trans-2-Butene

Rotation aboutC-C double bondis restricted

ConfigurationConfigurationPhysical properties:m.p; b.p

3.3.2 Naming Stereoisomeric Alkenes1. Naming by term Cis-trans

The same atoms or

atomic groups

on the same sides

on the opposite sides

of the double bond.

Prefixcis-

trans-

2. Naming by the E, Z Notational system

To disubstitutedAlkenes:

C CH

CH2CH2CH3H3C

CH3

C CCl

HBr

CH2CH3

P83, 3.4P83, 3.4

P175,Table 5.1

P175,Table 5.1

E, Z Notational systembase on an Sequence Rule （次序规则） － Cahn-Ingold-Prelog priority Rule1. Considering each of the double-bonded carbon, identify the two atoms directly attached and rank them according to atomic number.

C CCl

HBr

CH2CH3

Br > Cl, C > H

Lowpriority

Highpriority

E configuration: the high-priority groups are on the opposite sides of the double-bond

(E)-1-Bromo-1-chloro-1-butene(E)-1- 氯 -1- 溴 -1- 丁烯

(E)-1-Bromo-1-chloro-1-butene(E)-1- 氯 -1- 溴 -1- 丁烯

LowpriorityHigh

priority

Z configuration: the high-priority groups are on the same sides of the double-bond2. When two atoms directly attached to the double bond are identical, look at the second, third,or fourth atoms away from the double-bonded carbons until the first difference is found.

C CH

CH2CH2CH3H3C

CH3

(Z)-3-methyl-2-hexene(Z)-3- 甲基 -2- 己烯

(Z)-3-methyl-2-hexene(Z)-3- 甲基 -2- 己烯

C H

H

H

C C

H

H

H

H

H< C H

CH3

CH3

> C CH3

H

H

O H < C H

H

H

O

3. Multiple-bonded atoms are equivalent to the same number of single-bonded atoms.

C OH

CH O

O

The carbon isbonde to H, O, O

C CH

H

HC

H C

CC

H HThe carbon isbonde to H, C, C

C C + Br Br C C

Br Br

Organic Reactions:

The broken of original bonds,the formation of new bonds.

The broken of original bonds,the formation of new bonds.

P88, 3.6P88, 3.6

Starting material（原料）Substrate（底物）

Reagent（试剂）

Reagent（试剂）

ProductProduct

Reactants Reactants

A covalent bond may break in two way:

A B A + BHomolytic bond break(Radical)

( 均裂 )Homolytic bond break(Radical)

( 均裂 )

A B A + B Heterolytic bond break(Polar)( 异裂 )

Heterolytic bond break(Polar)( 异裂 )

CCl4

solvent

C C C

H

Reactional sites of alkene:The πbond is active and is readily attacked by the some reagents.

AdditionreactionAdditionreaction α- H is readily lostα- H is readily lost

3.4.1. Electrophilic Addition of Alkenes（亲电加成反应）

C C

π electrons lie above and below the plane ofdouble bond, soπ- bonded electrons are exposed ( 裸露 ).

π- bondπ- bond

The πbond is attacked by electron-seeking reagents － Electrophile （亲电试剂）

An reaction rule:Electronegative

species +Electropositive

species

(1) Addition of Hydrogen Halides ( 卤化氢 ) to Alkenes

C C + HX C C

H X+ HClCH3CH CHCH3 CH3CH2CHCH3

Cl2-Butene 2-Chlorobutane

Alkane halide

Alkane halide

P 109,4.1P 109,4.1

• Orientation of electrophilic addition: Markovnikov’s RuleCH3CH CH2 + HBr CH3 CH CH2

HBr+ CH3 CH CH2

H BrAddition to an unsymmetricallysubstituted alkenes:

Markovnikov’s Rule: In the addition of HX to an alkene, the H attaches to the carbon with fewer alkyl groups and X attaches to the carbon with more alkyl groups.

(80%) (20%)

Vladimir Vassilyevich Markovnikov

1838-1904

• Mechanism of the Reaction:

Step 1.

R2C CR2 + H X R2C CR2

H

+ X

The formation of the carbocation ( 正碳离子 )

Reactive intermediate

Reactive intermediate

Step 2.

The formation of the carbocation is the rate-determining step.

P92, 3.8P92, 3.8

R2C CR2

H

+ X R2C CR2

HX

slow

fast

H3C

CH3

CH3

C+ H3C

CH3

H

C+ H

CH3

H

C+ CH3+

> > >

• The stability of carbocations: P112, 4.3P112, 4.3

The one raison that stabilize a carbocation:the electron-donating effect of alkyl groups.

The structure of carbocations:

+C

R

R'R"

120°

The positively chargecarbon atom is sp2-hybridized,

The p orbital is vacant.The carbocation is trigonal plane.

Tertiary(3 ) > Secondary(2 ) > primary(1 ) > Methyl° ° °

• Regioselectivity ( 区域选择 性 ) of the reaction

P110, 4.2Ch.59

P110, 4.2Ch.59

The reaction that can proceed in morethan one direction, but actually in whichone direction is preferred.

Regiospecific ( 区域专一的 )

A more highly substituted carbocation ismore stable than a less highly substituted one.

+CH3 CH2

δ+ δ+

The electron-donating or electron-withdraw effect of a group that is transmitted through σbond.

Inductive effect( 诱导效应 ) of substituents:

P22,Ch.9P22,Ch.9

C CH2

CH3

CH3H

+

C CH2

CH3

CH3

+

H

Explanation for “Markovnikov’s rule”

C CH2 + HClCH3

CH3

Cl-

C CH2

CH3

CH3HCl

Cl-

C CH2

CH3

CH3 H Cl

(I)

(II)

The stabilities of carbocation:

(I) > (II)

Electrophilic addition to an unsymmetri-cally substituted alkene give the more highly substituted carbocation.

Electrophilic addition to an unsymmetri-cally substituted alkene give the more highly substituted carbocation.

CH3C

H

CH3

CH CH2

H

• Carbocation Rearrangements ( 重排 ) Ch.60,倒 7

Ch.60,倒 7

(40%) (60%)HCl

Cl-

(I)

(II)

Cl-

Stabilities of C+:

Tertiary > Secondary

Stabilities of C+:

Tertiary > SecondaryHydride-shift

CH3C

H

CH3

CH CH2HCl (CH3)2CHCHCH3

Cl

+ (CH3)2CCH2CH3

Cl0℃

CH3C

CH3

CH2 CH2

H

Problem:Propose a mechanism to account for the followingresult: + HBr

CH2CH3

Br

• Reactivity:

HI > HBr > HCl >> HFHI > HBr > HCl >> HF

Based on the ability to proton-donating

of HX

Alkenes?Alkenes?• Peroxide effect ( 过氧化物效应 )

An unsymmetric alkene reacts with HBr in the present of a peroxide (R-O-O-R), theAnti-Markovnikov addition occurs.

Ch.61,(d)Ch.61,(d)

H2C CHCH2CH3 + HBrR-O-O-R BrCH2CH2CH2CH3

(95%)

Free-redicaladditionFree-redicaladdition

（过氧化乙酰） （过氧化苯甲 酰）

CH3C C O

O

PhC C O CPh

O O

O OCCH3

O

(2) Addition of Sulfuric acid to AlkenesCh. 63, ( 丙 )Ch. 63, ( 丙 )

CH3 CH2CH + HO S

O

OH

O

Cold CH3 CH CH3

HSO4 CH3 CH CH3

OSO3H

H2O

HeatCH3 CH CH3

OHCold ConcentratedH2SO4

Cold ConcentratedH2SO4

Alkyl hydrogenSulfate( 硫酸氢酯 )

Hydrolysis( 水解作用 ):A bond is cleaved by reaction with water.Hydrolysis( 水解作用 ):A bond is cleaved by reaction with water.

Mono-substituted and Disubstituted alkenes:

Hydration ( 水合反应 )

RCH CH2

RCH CHR Ok!Ok!

(3) Acid-catalyzed Hydration of Alkenes

P114, 4.4

P114, 4.4( 酸催化的烯烃水合反应 )

(4) Hydroboration-Oxidation( 硼氢化 - 氧化 ) of alkenes

The method for preparation of the alcohols from anti-Markov. Adddition. The method for preparation of the alcohols from anti-Markov. Adddition. The hydroxyl group was added on lesssubstituted carbon.

CH3(CH2)7CH CH2 CH3(CH2)7CH2CH2OHOrganoboranes

( 有机硼烷 )Herbert Charles BrownGot the 1979 Nobel prize

Major method to prepare alcohols in industry

C C +H

H

H

HH2O

H2SO4(Cat.)

250 C°CH3CH2OH

Catalyst:Dilute H2SO4,H3PO4

Catalyst:Dilute H2SO4,H3PO4

Ch.66, Ch.66,

He discovered the hydroborationreaction (addition of diborane to alkenes) and developed the multi-faceted and synthetically useful chemistry of the resulting organo-boranes. In this photo, Professor Brown holds a model of 9-borabicyclo[3.3.1]nonane (9-BBN),prepared by adding borane to1,5-cyclooctadiene and itself a stable, useful hydroborating reagent. This work is summarized in Brown's book "Organic Synthesis via Boranes" (1975). Brown contri-buted to many other areas of organicchemistry, among which were selective reducing agents, steric effects (in displacement, elimination and acid-base reactions), and directive effects in electrophilic aromatic substitution (the σ+ constant).

Brown is perhaps the mostprolific organic chemist of the 20th century. He is best known for his work in organoboron chemistry, for which he shared (with G. Wittig) the 1979 Nobel Prize in Chemistry.

Brown is perhaps the mostprolific organic chemist of the 20th century. He is best known for his work in organoboron chemistry, for which he shared (with G. Wittig) the 1979 Nobel Prize in Chemistry.

Hydroboration :C C + BH

δ +δ -C C

H B

Electronegativity:H 2.1, B 2.0

Electronegativity:H 2.1, B 2.0

organoboraneReagent: boron hydride

B2H6B2H6 + O O BH3

THF( 四氢呋喃 )

Solvents ether: Et2O,

Diglyme: CH3OCH2CH2OCH2CH2OCH3

（二甘醇二甲 醚）CH3 CH2CH

δ +

BH2H

δ - CH3CH CH2

BH2H

δ - δ +

CH3CH CH2 (CH3CH2CH2)2BH

CH3CH CH2 (CH3CH2CH2)3B

borane

Oxidation: Hydrogen peroxide

(CH3CH2CH2)3BH2O2

OHCH3CH2CH2OH

Feature of the reaction:

Equal to the anti-Markov. Addition of H2O to alkenes

1. Regioselectivity: following Markov. Rule.2. Stereochemistry:

Syn-addition （顺式加成） : Two atoms or groups add to the sameface of a double bond.

C C + H Br C C

H Br

trans-2-Methylcyclo-pentanol

3. Non rearrangement

Syn-addition

Anti-addition （反式加成） : Two atoms or groups add to the opposite faces of a double bond.

C C + Br Br C C

Br

Br

The stereoselectivity of Hydroboration-Oxidation:

Problem: What products would you obtain from reaction of 1-ethylcyclopentenewith BH3,followed by H2O2,OH-?

Problem: What products would you obtain from reaction of 1-ethylcyclopentenewith BH3,followed by H2O2,OH-?

CH3 + 1/2 B2H6H

H2B

CH3

H

H2O2

OH

H

HO

CH3

H

(5) Addition of Halogen to AlkenesP116, 4.5

P116, 4.5

(CH3)2CHCH CHCH3 + Br2CCl4 (CH3)2CHCH CHCH3

Br Br0℃

Vicinal dihalide( 邻二卤代物 )

Solvents: CH2Cl2,CHCl3, Acetic acid

Identification for C=C.Identification for C=C.

Reagents: Cl2, Br2.

•Mechanism of the reaction:

Br Br¦Ä ¦Ä

C

CBr + Br

C

C

Step1.

C

CBrBr

C

C

Br

Br

Step2.Bromo-anionattacks from sideopposite.

Step 1 is the rate- determining step.

Bromonium ion ( 型离子 )

Step 1.

Step 2.

• Stereochemistry of halogen addition

Anti-addition

Br Br BrHH

Br

Br

H Br

H

(6) Conversion of Alkenes to Vicinal Halohydrin( 邻卤代醇 )

β- Halohydrin

Ch.63,( 丁 )Ch.63,( 丁 )C C + C C

X

X2 + H2O

OH

+ HX

Addition of halogen in aqueous solution.

Addition of halogen in aqueous solution.

Mechanism of the reaction:

CH3 CH2CHCl2

H2O

CH3 CH2

Cl

CH CH3 CH2CH

Cl

OH

Features of the reaction:

1. Following Markov. Rule, equal to the addition of one mole of HO-Cl+( 次氯酸 )

2. Anti-addition

3.4.2 Hydrogenation of Alkenes P118,4.6P118,4.6

+ heat

Catalyst: Pt,Pd, Ni

C C + H2Catalyst

C C

H H

r.t

Features of the reaction:1. An exothermic reactionBroken: πbond, H-H σbondFormation: 2 C-H σbond

Heat of hydrogenation:The heat evolved on hydrogenation of one mole. of an alkene.

The higher is the heat of hydrogenation,the less stable is the alkene.

The heat of hydrogenation is relative to the stability of alkenes.

Stability of alkenes:

CH2 CH2 < RCH CH2 < RCH CHR

< R2C CHR< R2C CR2 Cis- < Trans-

Ch.54,( 乙 )Ch.54,( 乙 )

Mechanism of alkene hydrogenation

2. The role of the metal catalystVery slowly without catalyst.

Changing the reaction path to lower activation energy （活化能） .

The addition of hydrogen to alkene is catalytic hydrogenation （催化氢化） .

3. Stereochemistry of Alkene hydrogenation

Alkene hydrogenation: syn-addition

CatalystCatalyst Hydrogen absorbedon catalyst surface

Hydrogen absorbedon catalyst surface

Complex of alkeneto catalyst

Complex of alkeneto catalyst

Mechanism of alkene hydrogenation

Insertion of hydrogeninto C=C

Insertion of hydrogeninto C=C

Alkaneproduct

Alkaneproduct

Regeneratedcatalyst

Regeneratedcatalyst

H2

H HC C

H H C CH

HC C

H H

+C CH

4. Heterogeneous reaction （异相反 应）Solvent （溶剂）： ethanol, hexane or acetic acid. To dissolve a alkeneMetal: solid

The reaction occurs at the interface of two phase. The reaction occurs at the interface of two phase.

CH3

CH3

H2, Pt CH3CH3

H

H

CH3COOH

Homogeneous( 均相）

3.4.3 Oxidation of Alkenes(1) Epoxidation of Alkenes ( 环氧化反应 )

P238, 6.18P238, 6.18

C C + R C

O

O O H C C +

O

R C

O

OH

Peroxy acid( 过氧酸 ) Epoxide

( 环氧化物 )Shapless, K. B.got the 2001 Nobel prize.

Solvents: acetic acid, CH2Cl2, CHCl3

Reagent: CH3 C

O

O O H

Peroxyacetic acid( 过氧乙酸 )

Preparation of epoxides from alkenesPreparation of epoxides from alkenes

K. Barry Sharpless, Ph.D. Organic/Inorganic ChemistThe Scripps Research Institutehttp://www.scripps.edu/chem/sharpless/cv.html

(2) Hydroxylation( 羟基化反应 ) of alkenes: Alkenes react with potassium perman-ganate or Osmium tetraoxide in basic solution to form 1,2-diols (glycol)( 二醇 ).

Cyclohexene cis-cyclohexanediol(37%)

syn stereochemistry.syn stereochemistry.

+ KMnO4NaOHH2O

OHOH

H

H

CH3CH CH2(1) OsO4, pyridine

(2) Na2SO3/H2OCH3CH CH2

OH OH

Cold solution of NaOH

NaHSO3

P120,4.7P120,4.7

Mechanism of the reaction:

C CKMnO4

C C

O O

MnO O

NaOHH2O

C C

OH OH

(3) Oxidative cleavage of alkenes:(A) Ozonolysis of Alkenes ( 臭氧化反应 )

Ch.70Ch.70O3(ozone) Ozonide Reducing agent: Zn

Hydrolysis Aldehydes or ketones

O3C C

O OO

Rearran-gement C

O

O OC

H2O

ZnC O + O C

Identification to the structure of a allkeneIdentification to the structure of a allkene

CCH3

CH3

CHCH31) O3

2) H2O, ZnC

CH3

CH3

O + O CCH3H

Ex.

2-Methyl-2-butene Acetone Acetaldehyde(B) With KMnO4 solution In hot OH- solution, neutral or acidicsolution:

Isopropylidene-cyclohexene

( 异亚丙基环己烯 )

Cyclohexa-none

( 环己酮 )

Acetone

CH3CH2CHCH CH2

CH3

+ KMnO4H2O CH3CH2CHC

O

CH3

+ CO2OH(45%)

CCH3

CH3+ KMnO4

H2O O + OCH3

CH3

3.4.5 Reaction of Alkenes with Alkenes: Polymerization

n CH2 CH2200¡æ, 200MPa

O2 or peroxide CH2CH2( )n

Polyethylene( 聚乙烯 )Ethylene: monomers

Polyethylene: polymer

Polymerization: many individual alkene molecules combine to give a high-molecular-weight product.

Polymerization: many individual alkene molecules combine to give a high-molecular-weight product.

nCH3

CH CH2

TiCl4 - Al(C2H5)3

50¡æ, 2MPa

CH3

CH CH2( )n

Ziegler – Natta catalyst

Received the 1963 Nobel

Prize

Received the 1963 Nobel

Prize

b. 1903d. 1979

"for their discoveries in the field of the chemistry and technology of high polymers"

Karl Ziegler Giulio Natta   1/2 of the prize 1/2 of the prize

Federal Republic of Germany Italy Institute of Technology Milan, Italy

Max-Planck-Institut for Kohlenforschung (Max-Planck-Institue for Carbon Research) M 黮 heim/Ruhr, Federal Republic of Germany

b. 1898d. 1973

The Nobel Prize in Chemistry 1963

http://www.nobel.se/chemistry/laureates/1963/index.html

Problems to Chapter 3:

P103:3.27(a): C C

HHH3CCHCH2CH3

CH3

(b)C CH H

CH3CH3CHCH2CH2CH

CH3 CH2CH3

3.28 (b)3.29 (e), (f)3.30 (a)3.323.33(b)3.353.39(b)3.413.42(c)

4.344.37(c), (e)(1)BH3,(2)H2O2,OH －

4.394.40(a),(c) Show the reac- tions.4.45(a), (b),(d)

(e)

4.50*4.57

4.344.37(c), (e)(1)BH3,(2)H2O2,OH －

4.394.40(a),(c) Show the reac- tions.4.45(a), (b),(d)

(e)

4.50*4.57

1. OsO42.NaHSO3

H

OH

OH

H

CH31. BH3

2.H2O2, OH

OH

H

CH3

H

Additional problems:1.Vinylcyclopropane reacts with HBr to yield a

rearranged alkyl bromide.Follow the flow of electrons as represented by the curve arrows,

show the structure of the intermediate in brackets, and show the structure of the final product.

H Br[ ]

Br? ?

2. Predict the products of the following reactions. Don’t worry about the size of the molecule, concentrate on the functional groups.

H3CH3C

HO

Br2 A?

B?HBr

1. OsO42.NaHSO3

C?

1. BH3,THF2.H2O2, OH D?

Cholesterol( 胆固醇 )

A look ahead: Problems to Chapter 4. AlkyneP146.4.25(b)4.26(b),(c)4.29(c)4.41 Show the reactions.4.424.444.45(c)4.484.524.56

A look ahead: Problems to Chapter 4. AlkyneP146.4.25(b)4.26(b),(c)4.29(c)4.41 Show the reactions.4.424.444.45(c)4.484.524.56