THE RELATIVE RATES OF BΛSE-CATALYSED HYDROGEN-DEUTERIUM EXCHANGE IN METHYL ETHYL KETONE

Abstract

The relative rates of hydrogen deuterium exchange at the α- and α' -positions in the simplest unsymmetrical ketone were determined by use of N.M.R. spectroscopy. It has been long held that in base-catalysed enolization processes the least alkyl substituted opposition is cost reactive. However it was observed that in the exchange reaction of 2-butanone catalyzed by OD- in D2O, the α- and α'-positions are similarly reactive while for weaker bases (p-NO2PHO-, AcO- ) the cost substituted α- position is the more reactive. The results are discussed in terms of a model for the transition state for enolization, and a continuity of mechanism between the acid-catalyzed, and base-catalyzed processes is proposed.