Nonlinear Hammett plot. Substituent effects in the substitution and elimination-rearrangement reactions of 1,1-diaryl-2-bromoethenes with potassium tert-butoxide in an aprotic solvent

Abstract

A series of 1, l-diaryl-2-bromoethenes was synthesized and allowed to react with potassium ¿-butoxide in anhydrous diglyme at 0°. The substitution products were isolated by solvent extraction and column chromatography and identified by nuclear magnetic resonance spectrometry and elemental analysis. The elimination-rearrangement products were identified by ultraviolet spectrophotometry. The rate constants for the rearrangements step were calculated by the time-ratio method. An increase in electron-withdrawing character of the substituent caused the elimination-rearrangement reaction to proceed slower and the substitution reaction to proceed faster. None of the compounds tested underwent both reactions. The Hammett reaction constant, p, was found to be