Functional Groups

C CC C C C

C

C

Br

C H

H

C

Cl

C C

C

C

OH

C H

C

C

I

alkene alkyne tertiaryhalogenoalkane

secondaryhalogenoalkane

primaryhalogenoalkane

tertiaryalcohol

Functional groups

C H

C

C

NHH

C H

C

C

NH

C H

C

C

NC

C C

O

H C C

O

CC O C

primaryamine

secondaryamine

tertiaryamine

ether aldehyde ketone

Functional groups

C C

O

O H C C

O

O C

C C

O

O C C

O

C C

O

Cl

C C

O

N

carboxylic acid ester amide

acid anhydride acyl chloride

C N

nitrile

Functional groups

H O

arene (benzene ring) phenol

Free Radical substitution

C HH

H

H

Cl Cl 2 Cl·

Initiation

Propagation

+ Cl· C·H

H

H

+ HCl

C·H

H

H

Cl Cl C ClH

H

H

+ Cl·+

C·H

H

H

·Cl C ClH

H

H

Cl· ·Cl Cl Cl

·C H

H

H

C·H

H

H

C H

H

H

CH

H

H

Free Radical Substitution

Termination

H (kJ mol-1) Eact (kJ mol-1)

Chain initiation

F2 2 F· +160 +160

Chain propagation

F· + CH4 HF + CH3· -134 +5

CH3· + F2 CH3F + F· -294 small

Overall

2 F2 + CH4 HF +CH3F -428

H (kJ mol-1) Eact (kJ mol-1)

Chain initiation

Cl2 2 Cl· +244 +244

Chain propagation

Cl· + CH4 HCl + CH3· +4.2 +16

CH3· + Cl2 CH3Cl + Cl· -107 small

Overall

2 Cl2 + CH4 HCl +CH3Cl -103

H (kJ mol-1) Eact (kJ mol-1)

Chain initiation

Br2 2 Br· +193 +193

Chain propagation

Br· + CH4 HBr + CH3· +69 +78

CH3· + Br2 CH3Br + Br· -101 small

Overall

2 Br2 + CH4 HBr +CH3Br -32

H (kJ mol-1) Eact (kJ mol-1)

Chain initiation

I2 2 I· +151 +151

Chain propagation

I· + CH4 HI + CH3· +130 +141

CH3· + I2 CH3I + I· -84 small

Overall

2 I2 + CH4 HBr +CH3I +46

bonding in alkenes

C C HH

HH

Two adjacent p orbitalsoverlap to produce a bond

The exposed electron pair can be attacked by electrophiles.

An electrophile is a species with an empty orbital that can accept a pair of electrons.

Electrophilic addition to alkenes

Reagent Electrophile (in bold)

Product of reaction with propene

Br2 (in organic solvent) Br Br

+ -

CH3CHBrCH2Br

Br2 (aq) CH3CH(OH)CH2Br

HBr

H+

CH3CHBrCH3

cold H2SO4 (l) CH3CH(OSO3H) CH3

Addition of HBr to propene

C C

CH3 H

H H

H Br+ C C

CH3 H

H H

H+

Br-

C C

CH3 H

H H

HBr

Markovnikov’s rule:

The less electronegative atom (H) adds to the carbon atom of the double bond with most H atoms attached. This gives rise to a more stable carbocation intermediate (order of stability 1°<2°<3°)

Addition of Br2 to propene

C C

CH3 H

H H

Br Br+ C C

CH3 H

H H

Br+

Br-

C C

CH3 H

H H

BrBr

Br2 is non-polar but as it approaches the bond, a dipole is induced.

Addition of Br2 (aq) to propene

C C

CH3 H

H H

Br Br+ C C

CH3 H

H H

Br+

Br-OH2

C C

CH3 H

H H

BrH2O+

C C

CH3 H

H H

BrHO

H+ (aq)

Other alkene reactions

Addition of hydrogen

CH3CH=CH2 + H2 (g) → CH3CH2CH3 (Ni catalyst, 200°C)

Oxidation

CH3CH=CH2 CH3CH(OH)CH2OH

Purple KMnO4 (aq) is decolourised by alkenes

KMnO4 (aq), H2SO4

(cold)