An addition reaction, in organic chemistry, is in its simplest terms an organic reaction where two or more molecules combine to form a larger one.[1][2]
Addition reactions are limited to chemical compounds that have multiply bonded atoms, such as molecules with carbon-carbon double bonds, i.e., alkenes, or with triple bonds, i.e., alkynes. Also included are molecules containing carbon—hetero double bonds like those with carbonyl (C=O) groups or those with imine (C=N) groups.
There are two main types of polar addition reactions: electrophilic addition and nucleophilic addition. Two non-polar addition reaction exists as well called free radical addition and cycloadditions.
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 reactions are also encountered in polymerizations and called addition polymerization.
In the related Addition-elimination reaction an addition reaction is followed by an elimination reaction. In the majority of reactions it involves addition of poti to carbonyl compounds in what is called nucleophilic acyl substitution.[3]
Other addition-elimination reactions are the reaction of an aliphatic amine to an imine and an aromatic amine to a Schiff base in alkylimino-de-oxo-bisubstitution. The hydrolysis of nitriles to carboxylic acids is also a form of addition-elimination.
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