Mechanisms in Organic Chemistry

Alkenes Aldehydes or ketones

Halogenoalkanes Arenes Alkanes

Electrophilic

AdditionHBr, Br2,Br2(aq)

Free Radical

Polymerisation

Nucleophilic Addition

Nucleophilic Substitution

SN1

SN2

Electrophilic Substitution

Free Radical Substitution

Electrophilic Addition 1 – Ethene + HBr

H

Br _

+

CC

H

H

H

H H+

:Br_

CC

H

Br H

H

H HC C

H

H H

H

home

Electrophilic Addition 2 – Ethene + Br2(hexane)

Br

Br _

+

CC

H

Br

H

H H+

:Br_

CC

H

Br Br

H

H HC C

H

H H

H

home

Electrophilic Addition 3 – Ethene + Br2(aq)

Br

Br _

+

CC

H

Br

H

H H+

:OH2

CC

H

OH Br

H

H HC C

H

H H

H

home:Br_

HBr

Nucleophilic Addition – Reaction of HCN with Carbonyls

C

O

H3C H

C

:O_

H3C H

CN

C

:OH

H3C H

CN

H+

:CN_

+

_

home

C CH3

CH3

H3C

OH

C CH3

CH3

H3C

Br

C CH3

CH3

H3C +

:Br-

+

- :OH-

Nucleophilic Substitution – SN1 Mechanism

Rate = k[C4H9Br]home

CC

H

H H

H

H Br CC

H

H H

H

H OH

:OH-

Nucleophilic Substitution – SN2 Mechanism

Rate = k[C2H5Br][:OH-]

:Br-

home

+ _

(NB Transition state)

Electrophilic Substitution 1 – Nitration of benzene

H2SO4 + HNO3 NO2+ + HSO4

- + H2O

home

+

NO2H+NO2NO2

H+

Electrophilic Substitution 2 – Bromination of benzene

Br2 + AlCl3 Br+ + AlBrCl3-

home

+

BrH+Br Br

HBr

AlCl3

Electrophilic Substitution 3 – Alkylation of benzene

CH3Cl + AlCl3 CH3+ + AlCl4

-

home

+

CH3H+CH3CH3

HCl

AlCl3

Electrophilic Substitution 4 – Acylation of benzene

CH3COCl + AlCl3 CH3CO+ + AlCl4-

home

+

CH3C

O

HCH3+C

OCH3C

O

HCl

AlCl3

Br+

Bromination of methylbenzene – ring substitution

AlBr3

HBr

Br2 + AlBr3 Br+ + AlBr4-

CH3

Br

home

CH3CH3

+

H

Br

Free Radical Substitution 1 – Methane + Cl2

Initiation Cl Clu.v. light

2Cl.

PropagationCH4 + Cl

.

. CH3 + HCl

. CH3 + Cl2 CH3Cl + Cl

.

Termination . CH3 +

. CH3

C2H6

. CH3 +

. Cl

CH3Cl home

Free Radical Addition Polymerisation of Ethene

home

RC C

H

H H

H

C C

H

H H

HCC

H

H H

H

R

CC

H

H H

H

R

CC

H

H H

H

R CC

H

H H

H

Propagation

InitiationR R

heat

2R.