Secondary carbon-13 isotope effect on the ionization of benzoic acid
Abstract
The effect of carbon-13 enrichment in the carboxyl group on the dissociation constant of benzoic acid has been determined in the temperature range of 10–30 °C. The isotope effect, K12/K13, decreases from 1.003 at 10 °C to 1.001 at 30 °C. The temperature dependence of the equilibrium isotope effect, measured by e.m.f. methods, could not be reproduced theoretically. The disagreement between experiment and theory is explained by means of a superimposed isotope effect due to solvation.