Variational transition state theory rate constants and H/D kinetic isotope effects for CH3 + CH3 OCOH reactions.

Abstract

The rate constants and H/D kinetic isotope effect for hydrogen abstraction reactions involving isotopomers of methyl formate by methyl radical are computed employing methods of the variational transition state theory (VTST) with multidimensional tunneling corrections. The energy paths were built with a dual-level method using the moller plesset second-order perturbation theory (MP2) method as the low-level and complete basis set (CBS) extrapolation as the high-level energy method. Benchmark calculations with the CBSD-T approach give an enthalpy of reaction at 0 K for R1 (-4.5 kcal/mol) and R2 (-4.2 kcal/mol) which are in good agreement with the experiment, that is, -4.0 and - 4.8 kcal/mol. For the reactional paths involving the isotopomers CH3 + CH3 OCOH → CH4 + CH3 OCO and CH3 + CH3 OCOD → CH3 D + CH3 OCO, the value of kH /kD (T = 455 K) using the canonical VTST/small-curvature tunneling approximation method is 6.7 in close agreement with experimental value (6.2). © 2019 Wiley Periodicals, Inc.