The stereochemical requirements of concentrated pericyclic reactions

Abstract

A concerted reaction is one in which the conversion of reactants (R) into the products (P) occurs directly by way of a single transition state (T.S.). An exothermic concerted reaction is represented by the potential energy profile of Fig. 3.1(a). When the conversion of reactants into products proceeds by way of more than one transition state, such that one or more intermediates (I) are formed, the processes are accordingly non-concerted. A two-step process involving one (metastable) intermediate is represented by Fig. 3.1(b). However, since each elementary step of any chemical reaction must be concerted, by definition, then case (b) may be divided into the two concerted sequences: R→I and I→P.