CARBON-13 ISOTOPE EFFECTS IN NUCLEOPHILIC ALIPHATIC DISPLACEMENT REACTIONS

Abstract

Carbon-13 isotope effects have been measured for the solvolysis reactions of 1-brorao-l-phenylethane in methanol and ethanol and for the bimolecular reaction of this halide and benzyl bromide with alkoxide ion. For the unimolecular displacements, the rate constant has been found to be 1.006, which corresponds to an isotope effect of 0.6 per cent. Rate constant ratios, observed of 1.003 and 1.053 have been for the reaction of 1-bromo-l-phenylethane with ethoxide ion and of benzyl bromide with methoxide ion, respectively. Extensive tests have been performed to establish that the reactions wore unidirectional under the conditions used and that the experimental procedures were uncomplicated by exchange, rearrangement, or isotopic fractionation. The results have been discussed in terms of the Bigeleisen expression for the theoretical calculation of isotope effects.