The Mechanism of Bimolecular β‐Elimination Reactions

Abstract In bimolecular β‐elimination (E 2 mechanism), several bonds are ruptured or formed in one concerted reaction step. However, the various aspects of bond‐making or ‐breaking need not be completely synchronous. In the E 2 transition state for elimination HX, rupture of the CX bond may be more advanced than that of the CH linkage, or vice versa. Factors influencing the relative extents of rupture of these two bonds at the transition state are discussed, and the consequences of non‐synchroneity in one sense or the other are developed from theory and illustrated from experiment. This treatment provides an understanding of the Hofmann‐vs.‐Saytzeff orientation problem.