Comportamento não-arrhenius no rearranjo do 1,2-h metilclorocarbeno: tunelamento quântico vs canais reativos competitivos

Abstract

According of their structural composition, carbenes are highly reactive species. Thus, they are often observed in chemical reactions in the form of short-lived reactive intermediates and the kinetics of the processes involving these species do not occur in a trivial way. The purpose of this work is to demonstrate the kinetic behavior of the intramolecular rearrangement of the H atom in the methylchlorocarbene molecule, taking into account the temperature dependence. Previous works have pointed an upward curvature (sub-Arrhenius), characterizing a deviation from the linearity in the Arrhenius plot. A series of hypotheses were conditioned to this behavior, among them: competitive paths; reaction in the excited state; quantum tunneling; variable transition states, however, these studies were inconclusive. For a more descriptive understanding of the reaction kinetics of this process, we performed a set of semi-quantum simulations through Car-Parinello and Path Integrals molecular dynamics which identified several reactional paths. Additionally, the geometry, energy and frequencies of the stationary points of the mechanisms obtained by the molecular dynamics were calculated electronically at B3LYP (CC-PVDZ, AUG-CC-PVTZ), B2PLYP (6-311 ++ G *, CC -PVTZ) and WB97XD (AUG-CC-PVDZ) levels of calculation. The absolute kinetic constant for the hydrogen atom migration reaction was also calculated at the same levels. The results obtained in this study suggest that the sub-Arrhenius behavior is mainly due to the tunneling effect on the intramolecular rearrangement of the methylchlorocarbene molecule, excluding competitive mechanisms effects.