All chemical reactions involve bond making (fusion) and bond breaking (fission). Chemical bonds (naively) consist of pairs of electrons shared between two atoms. When a bond breaks, the electrons which form that bond can either split evenly (homolytic) or unevenly (heterolytic) between the two atoms connected by the bond.

Homolytic fission:


Heterolytic fission:


Electrophiles

and nucleophiles




Alkanes
Free-radical substitution
The reaction of methane with chlorine as a free-radical substitution mechanism

Initiation


propagation and

termination steps.



Alkenes
Electrophilic addition reactions of alkenes with HBr, H2SO4 and Br2
symmetrical/assymmetrical alkenes with bromine: alkene -> dibromo-alkane
symmetrical/assymmetrical alkenes with hydrogen bromide: alkene -> bromo-alkane
symmetrical/assymmetrical alkenes with sulphuric acid: alkene -> alcohol
Acid catalysed hydration of alkene with concentrated phosphoric acid

Halogenoalkanes
Nucleophilic substitution
Halogenoalkanes undergo substitution reactions with the nucleophiles OH–, CN– and NH3, and subsequent reactions with generated primary amine, secondary amine, tertiary amine - prevent subsequent reactions with a large excess of ammonia initially.
Elimination
The concurrent substitution and elimination reactions of a halogenoalkane (eg 2-bromopropane with potassium hydroxide).
Elimination of Halogenoalkanes with ethanolic hydroxide ions

Alcohols
Elimination
Alkenes can be formed from alcohols by acid-catalysed elimination reactions

Aldehydes and ketones
Aldehydes can be reduced to primary alcohols, and ketones to secondary alcohols, using NaBH4 in aqueous solution. These reduction reactions are examples of nucleophilic addition.
The nucleophilic addition reactions of carbonyl compounds with KCN, followed by dilute acid, to produce hydroxynitriles.
Aldehydes and unsymmetrical ketones form mixtures of enantiomers when they react with KCN followed by dilute acid.

Acylation
Students should be able to outline the mechanism of nucleophilic addition–elimination reactions of acyl chlorides with water, alcohols, ammonia and primary amines.

Aromatic chemistry
Students should be able to outline the electrophilic substitution mechanisms of:
nitration, including the generation of the nitronium ion
friedel-craft acylation using AlCl3 as a catalyst.

Amines
The nucleophilic addition–elimination reactions of ammonia and primary amines with acyl chlorides and acid anhydrides.
Students should be able to outline the mechanisms of:
these nucleophilic substitution reactions
the nucleophilic addition–elimination reactions of ammonia and primary amines with acyl chlorides.