A study of the mechanism of solvoysis of but-3-enyl bromide (4-bromobut-1-ene) using the extended (two-term) Grunwald–Winstein equation

Abstract

The solvolysis of but-3-enyl bromide at 70 °C follows the S_N2 mechanism over a wide variety of solvent as indicated by a sensitivity to changes in solvent nucleophilicity (l value) of 0.99 ± 0.04, specific rates of solvolysis of about on-half of those for the saturated butyl bromide and a k_OTs/k_Br ratio in ethanol of 12, essentially indentical with the value previously observed for ethanolyses of methyl and ethyl derivatives. There are indications of a minor (about 35%) S_N1 component to the solvolysis in 97% TFE, which becomes dominant in 90% HFIP. Kinetic analysis suggest, consistent with previous product studies, only an approximately 4% S_N2 component to a dominant S_N1 formolysis of the corresponding tosylate.