Ions and Ion Pairs. Their Meaning and Significance in Organic Reactions

Abstract

Abstract A brief survey of the developments leading to the concept of ion pairs and of still higher ionic aggregates is followed by detailed discussion of its physical meaning. The distinction between contact ion pairs and covalently bonded molecules is clarified by comparing gaseous dissociation processes with those taking place in solution. Such a comparison reveals clearly the significance and the role of solvent molecules in homolytic and heterolytic dissociations. In the following discussion it is pointed out that a variety of ion pairs may be formed from the pair of oppositely charged ions. An attempt is made to explain under what conditions the structurally different ion pairs may be treated as distinct species and when such a distinction fails. Finally, examples are given to demonstrate how the structural changes of ion pairs nature may affect the rates and the equilibria of reactions in which they participate, an effort being made to provide examples pertaining to polymerization processes.