Abstract

Halogenation modifies the pharmacological properties and uses of a host of compounds. This is accomplished at the molecular level by different mechanisms, several of which are understood. Even when the mechanism by which the halogen exerts its influence is poorly (or not at all) understood, the halogen can often be replaced by other substituents which sometimes are equivalent spatially on electronically, but sometimes it is equally well replaced by groups which seem quite different. Although there are a few cases where the halogen per se is essential, in most cases halogenation is merely the most economic on expedient means to achieve a given electronic or stenic influence.