Isotope Effects as Tools for the Elucidation of Reaction Mechanisms

Model calculations, based on the statistical-mechanical formulation of isotope effects, have been used to predict how analyses of experimentally measured isotope effects may be used to gain information concerning the differences between the reactants and the transition state in a rate process or between the reactants and the products in an equilibrium process. It is shown that while isotope effects cannot be used generally to obtain reliable information about geometry differences, they can be used to determine or set limits on force constant differences and possibly to gain insight into the nature of reaction coordinates. Information of this type can be useful in the elucidation of reaction mechanisms. A method by which isotope effects for large molecular systems may be studied theoretically by working with smaller model molecules is presented.