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The kinetics of hydrogen atom abstraction reactions of methyl difluoroacetate (CF2HCOOCH3) by OH radical has been studied by quantum mechanical method. The geometry optimisation and frequency calculation of the titled compound was performed with density functional theory using hybrid meta density functional MPWB1K with 6-31+G(d,p) basis set. Transition states have been determined and intrinsic reaction coordinate (IRC) calculation has been performed to ascertain that the transition from reactants to products was smooth through the corresponding transition state. Energy values are refined by making single point energy calculation at G3B3 level of theory and an energy level diagram is constructed. The standard enthalpies of formation of reactants and other species formed during the reaction were calculated using isodesmic method. The rate constants are calculated using canonical transition state theory and the overall rate constant is determined to be 1.35×10−13cm3molecule−1s−1at 298 K and 1 atmospheric pressure. Tunnelling has been taken into account in the determination of the rate constant because it plays a critical role at low temperature especially when transfer of hydrogen takes place. The calculated value is found to be in good agreement with the experimentally determined value of 1.48×10−13cm3molecule−1s−1. [ABSTRACT FROM PUBLISHER]

The present work deals with the theoretical investigation on the Cl initiated H-atom abstraction reaction of sevoflurane, (CF)CHOCHF. A dual-level procedure has been adopted for studying the kinetics of the reaction. Geometrical optimization and frequency calculation were performed at DFT(BHandHLYP)/6-311G(d,p) while single-point energy calculation was made at CCSD(T)/6-311G(d,p) level of theory. The intrinsic reaction coordinate (IRC) calculation has also been performed to confirm the smooth transition from the reactant to product through the respective transition state. The rate constants were calculated using conventional transition state theory (TST). It has been found that 99 % of the reaction proceeded via the H-atom abstraction from the -CHF end of the sevoflurane. The rate constant of the dominant path is found to be 1.13 × 10 cm molecule s. This is in excellent agreement with the reported experimental rate constant of 1.10 × 10 cm molecule s obtained by relative rate method using FTIR/Smog chamber and LP/LIF techniques. [ABSTRACT FROM AUTHOR]