Addition reaction

An addition reaction, in chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one.

There are two main types of polar addition reactions:
 * Electrophilic addition
 * Nucleophilic addition

Other non-polar addition reactions exists as well:
 * Free radical addition

Addition reactions are limited to chemical compounds that have multiply-bonded atoms:
 * Molecules with carbon-carbon double bonds or triple bonds
 * Molecules with carbon - hetero double bonds like C=O or C=N

An addition reaction is the opposite of an elimination reaction. For instance the hydration reaction of an alkene and the dehydration of an alcohol are addition-elimination pairs.

Addition-elimination reaction
In the related Addition-elimination reaction an addition reaction is followed by an elimination reaction. In the majority of reactions it involves addition of nucleophiles to carbonyl compounds in what is called nucleophilic acyl substitution.

Other addition-elimination reactions are:
 * reaction of an aliphatic amine to an imine and an aromatic amine to a Schiff base in alkylimino-de-oxo-bisubstitution
 * Hydrolysis of nitriles to carboxylic acids