Elimination reactions to give alkenes

This chapter focuses on elimination reactions to give alkenes. There are two principal alkene-forming reactions from alkyl halides which closely parallel SN2 and SN1 mechanisms. One is bimolecular and concerted, the other is stepwise with an initial unimolecular step. Both reactions overall involve a base and the elimination of HX from a molecule where X is either halogen or another nucleofuge bonded through a hetero-atom to the α-carbon. The chapter then looks at two other mechanisms for the elimination of HX. One is stepwise and involves a base, the other is a thermally induced single-step unimolecular mechanism which does not involve a base. Finally, the chapter considers briefly the mechanism of a nucleophile-induced reaction which yields alkenes though not by the elimination of HX, but X2.