Illustrated Glossary of Organic Chemistry

E2 mechanism (E2 reaction): An elimination reaction mechanism in which three bond changes occur simultaneously: carbon-leaving group bond scission, pi bond formation, and deprotonation by base. In the most common E2 mechanism, the proton removed is beta to the leaving group; this type of elimination is called beta elimination. Removal of an alpha hydrogen (alpha elimination) usually leads to a carbene.

A concerted, intermolecular E2 reaction.

A nonconcerted, intramolecular E2 reaction.