Elimination reactions of 1,2-diaryl-1-chloroethanes promoted by sodium ethoxide in ethanol. The kinetic effects of α- and β-phenyl substituents

Abstract

The kinetics of the elimination reactions of several substituted 1,2-diaryl-1-chloroethanes promoted by sodium ethoxide in ethanol have been studied. On the basis of the kinetic effects of β-phenyl substituents a ρ value of +2·26 has been calculated. This value is slightly less positive than that (+2·50) found in the corresponding elimination from substituted phenylethyl chlorides, thus showing that the introduction of an α-phenyl group does not modify substantially the carbanionic character of the transition state in the elimination reactions of β-phenyl activated substrates. Small kinetic effects are observed for α-phenyl substituents. Electron-withdrawing α-phenyl substituents produce an increase in the reaction rate: it appears therefore that these substituents exert their influence mainly through a favourable interaction with the partial negative charge present on C_β in the transition state.