Elimination Reactions in Organic Chemistry

When a molecule possesses a good leaving group, the two most common reaction classes at sp3 centers are the substitution and elimination reactions of the alkyl halides and pseudo halides. Like the substitution reactions, the elimination reactions are classified in kinetic terms as either unimolecular (E1) or bimolecular (E2).

When a good leaving group is present it is mainly there, from a synthetic standpoint, to replace it with something else or to increase the functionality of the compound by one carbon to form an alkene by just getting rid of it. There are two pathways of reaction for weak bases which are called good leaving groups on organic molecules and besides substitution, the other pathway is elimination, where the group (often a halide or halogen substituent) and a hydrogen atom are removed through a route known as β-elimination from the molecule to form a double bond or alkene.

The molecularity of a reaction is a term in chemical kinetics that refers to the number of species that come together to react in the rate-determining or slow step of a reaction. In the case of β-elimination, the reaction is a Bronsted acid-base reaction and therefore involves the transfer of a hydrogen ion (a proton) from an acid to a base.