The substituent dependence of the primary deuterium kinetic isotope effect in elimination from phenethyl bromides and dimethyl(phenethyl)-sulphonium bromides in 50·2 mole % dimethyl sulphoxide–water

Abstract

Primary deuterium kinetic isotope effects (K₂^H/K₂^D) have been determined for 1,2-elimination from a series of substituted phenethyl bromides and dimethyl(phenethyl)sulphonium bromides in 50·2 mole % Me₂SO–H₂O. A maximum in the K₂^H/K₂^D ratio was observed for the phenethyl bromides but the existence of a maximum could not be determined for the dimethyl(phenethyl)sulphonium bromides. Some evidence for proton tunnelling is presented for the p-methoxy-compounds. Hammett ρ values were determined and the value was larger for the poorer leaving group.