Dynamics of hydride transfer in solution using variational transition state theory

A family of global potential energy surfaces has been generated to mimic a large and diverse body of experimental results for hydride transfer between NAD{dollar}sp+{dollar} analogues. The first potential energy surfaces are collinear three-body models (A{dollar}sb{lcub}rm i{rcub}{dollar}-H-A{dollar}sb{lcub}rm j{rcub}{dollar}){dollar}sp+{dollar} of the reactive systems, where A{dollar}sb{lcub}rm i{rcub}sp+{dollar} and A{dollar}sb{lcub}rm j{rcub}sp+{dollar} are intended to mimic NAD{dollar}sp+{dollar} analogues. Improved canonical variational transition state theory with large curvature ground-state tunneling was used to calculate rate constants. These rate constants were fitted to Marcus theory just as if they were experimental rate constants. These potential energy surfaces were used to examine the criteria of tunneling, which includes the magnitude of the KIE, several aspects of the the temperature dependence of the KIE, the value of the exponent, r, in the Swain-Schaad relation, and the response of the KIE to changes in the reaction equilibrium constant. The variational effect on the KIE, which reduces the quasi-classical contribution to the KIE has also been examined. Tunneling tends to increase E{dollar}sb{lcub}rm a{rcub}{dollar}(D)-E{dollar}sb{lcub}rm a{rcub}{dollar}(H) and decrease A(H)/A(D). Variational effects work in the opposite direction. Nevertheless, careful measurements of the Arrhenius parameters should be able to detect tunneling when k{dollar}sb{lcub}rm H{rcub}{dollar}/k{dollar}sb{lcub}rm D{rcub}{dollar} {dollar}ge{dollar} {dollar}sim{dollar}6. The Swain-Schaad relation appears to apply to the computed rate constants but does not appear to be useful to identify tunneling.; The second family of potential energy surfaces is for a 9-body model (CH3-H-CH3){dollar}sp+{dollar} of the reactive system. In addition to the analogous 3-body results, the secondary {dollar}alpha{dollar}-deuterium KIE has been studied. Experimental values of the secondary KIE's and the trend of the secondary KIE's with isotopes in-flight, H or D, have been reproduced. The secondary KIE's were factored to understand the contributions from vibrational modes, rotational modes, the variational effects, and the tunneling effects, separately. The umbrella mode of vibration as well as the stretching mode are important not only to the value of the primary KIE but also to the secondary KIE.; This study clearly demonstrates that Marcus theory can be reproduced by modern generalized transition state theory with large curvature ground-state tunneling, which provides a good understanding of the KIE's in the hydride transfer reactions.