Factors Affecting the Transition State in Acetate-Catalyzed Enolization. The Influence of Methyl and Bromine Substituents on the Rate of Bromination of Acetone

Abstract

<p> The acetate-catalyzed bromination of acetone is shown to occur by an enolization mechanism, although the reactions involved in this process are more complex than has been supposed.</p> <p> A study of the activation parameters for the enolization of some bromoacetones, and an observed linear free energy relationship between enolization rate constants, and acid ionization constants, shows that the transition state for this process resembles enolate and not enol.</p> <p> Bromine substitution in ketones accelerates enolization rates on both sides of the carbonyl group.</p> <p> The acetate-catalyzed enolization of 2-butanone favours the methylene group by a factor of nearly two. This fact is interpreted in terms of methyl groups being inductively electron-withdrawing in their effect in forming an enolate transition state.</p>