Ab initio calculations of activation energy of the reaction of hydrogen exchange on strongly acidic centers

Abstract

Ab initio calculations of fragments of the potential energy surfaces of hydrogen exchange reactions between H2, CH4, and alanine molecules and the H3O+ ion were performed by the restricted Hartree-Fock method, at the second-order Moller-Plesset level of perturbation theory, and by the method of coupled clusters using the 6–31G* and aug-cc-pVDZ basis sets. The one-center synchronous mechanism of hydrogen exchange reaction was studied and the activation energies and structures of transition states were determined. It was found that the geometric parameters of the H2 and CH4 molecules in the transition states are close to those of the H3 + and CH5 + ions. The higher the proton affinity of the reacting molecule in the reaction studied the lower the activiation energy of hydrogen exchange. The one-center mechanism studied can be used to describe the high-temperature solid-state catalytic isotope exchange (HSCIE) reaction. The results ofab initio calculations of synchronous hydrogen exchange between the H3O+ ion and hydrogen atoms in different positions of the alanine molecule are in good agreement with experimental data on the regioselectivity and stereoselectivity of the HSCIE reaction with spillover-tritium.