Direct dynamics study on the hydrogen abstraction reaction of fluoromethanes with vinyl radical

Abstract

A direct dynamics method has been employed to predict the kinetic feature of the hydrogen abstraction reactions of vinyl radical (C2H3) with different fluoromethanes (CH2F2 and CHF3). The required potential energy surface information for the kinetic calculation was obtained at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311G(d,p) dual-level. The calculated reaction energies are −8.3kcal/mol for the hydrogen abstraction reaction of CH2F2 with C2H3, −3.2kcal/mol for the abstraction of CHF3 with C2H3, and the two potential barriers are 9.4 and 10.4kcal/mol, respectively. The rate constants were evaluated by means of the conventional transition-state theory (TST), the canonical variational transition-state theory (CVT) with or without small-curvature tunneling (SCT) correction over the temperature range of 200–3000K. The dynamics calculations indicate that both the rate constants of the two hydrogen abstraction reactions exhibit a positive temperature dependence, in which the variational effect is negligible, whereas the tunneling effect is only considerable in the lower temperature range. Agreement between the calculated and documentary data available is good. In addition, the effects of fluorine substitution on the potential barriers and the rate constants for this class of reactions were examined.