Topic summary
Elimination reaction
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step reaction mechanism. The most common types of reaction mechanisms are a one-step mechanism known as the E2 reaction and a two-step mechanism is known as the E1 reaction. The numbers in the Hughes–Ingold symbols refer not to the number of steps in the mechanism, but rather to the molecularity of the reaction kinetics: E2 is bimolecular (second-order) while E1 is unimolecular (first-order). In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists. Finally, the pyrolysis of xanthate and acetateesters proceed through an "internal" elimination mechanism, the Ei mechanism. All of these reactions involve loss of sigma bonded groups to form a pi bond on the structure, such as loss of hydrogen and halogen atoms from an alkane to form an alkene.