Leffler relationship of the gem-dimethyl effect

Abstract

The established Leffler relationship of the gem-dimethyl effect allows: (a) the steric substituent effects upon ring closure and opening to be divided into two contributions, a ‘general gem-dimethyl effect’ linearly correlated to the equilibria of the reaction and additional strains with some substituents due to the steric requirements of the reaction centre in the transition state, and (b) the coefficients of the Leffler equation to be used in characterizing the transition state structure.