An addition reaction, in chemistry, is in its simplest terms a 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
• concerted reactions

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=0 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 a addition-elimination pair.

See also

Application of addition reactions in addition polymerization.