Illustrated Glossary of Organic Chemistry

Addition reaction: A reaction in which atoms or groups are added to opposite ends of covalent bond, usually a pi bond, but sometimes a sigma bond.

Addition of HBr to a the carbon-carbon pi bond of an alkene results in new C-H and C-Br bonds on opposite ends of the alkene pi bond.


Addition of HBr to a carbon-carbon sigma bond of a cyclopropane ring results in new C-H and C-Br bonds where the cyclopropane carbon-carbon bond was ruptured.