Theoretical kinetic isotope effects for the hydride transfer from formate to carbon dioxide: A comparison of theory with experiment

Abstract

AbstractHeavy atom and deuterium isotope effects for the hydride transfer from formate to carbon dioxide were determined using MNDO, AM1, and PM3 semiempirical methods and the ab initio RHF/3‐21G*, 3‐21 + G, 6‐31G*, and 6‐31 + G* basis sets. Frequencies were also determined for ground state structures using 6‐31G* basis set at the MP2 level of theory. The calculated isotope effects compared favorably with the experimentally determined values of Hermes et al. (Biochemistry, 23, 5479 (1984)). The calculated ground state frequencies were high for most vibrational modes as compared with measured values, however some ab initio methods underestimate the carbon hydrogen stretching frequencies. The heavy atom isotope effects were influenced to a large extent by the excitation factor, the mass factor and the moment of inertia factor of the Bigeleisen equation.