Addition reaction

An addition reaction, in organic chemistry, is a reaction driven by electrophilic and nucleophilic mechanism. Where the double or triple bond attacks and electrophile producing a carbocation intermediate or a haloni ion intermediat. In most cases, trans- isomers are observed due to a halonium ion intermediate rather than a carbocation intermediate. The product results in the addition of new atoms and no by products.

Addition reactions are limited to chemical compounds that have multiple bonds, such as molecules with carbon–carbon double bonds (alkenes), or with triple bonds (alkynes), and compounds that have rings, which are also considered points of unsaturation. Molecules containing carbon—hetero double bonds like carbonyl (C=O) groups, or imine (C=N) groups, can undergo addition, as they too have double-bond character.

An addition reaction is the reverse of an elimination reaction. For instance, the hydration of an alkene to an alcohol is reversed by dehydration.

There are two main types of polar addition reactions: electrophilic addition and nucleophilic addition. Two non-polar addition reactions exist as well, called free-radical addition and cycloadditions. Addition reactions are also encountered in polymerizations and called addition polymerization.

General overview of addition reactions. Top to bottom: electrophilic addition to alkene, nucleophilic addition of nucleophile to carbonyl and free-radical addition of halide to alkene

Depending on the product structure, it could promptly react further to eject a leaving group to give the addition–elimination reaction sequence.