Effects of Isotopic Substitution on thermal rate constants for the Hydrogen Abstraction Reactions H3COCOH + O
Chemical Kinetics, Transition State, Combustion Reactions, Coupled-Cluster, DFT.
In this study, the energetic, structural and spectroscopy parameters of the stationary points generated by the hydrogen abstraction reactions of X+ X3COC(=O)X, in which X = H or D, were obtained at DFT/BB1K/maug-cc-pVTZ, level of theory. At this level, the height of the classical barriers, V‡, for R1 and R2, were 10,45 and 12,05 kcal/mol, respectively. In the aspect of chemical kinetics and dynamics, the thermal rate constants were determined using the CVT/SCTapproach, in a wide temperature range (T = 250 - 2000 K). At low temperatures, the quantum tunneling plays an important role in the k(T). At 250 K, for example, the CVT/SCT thermal rate constant (3,27x10-15 cm3molécule-1s -1) is 557,08 times greater than TST counterpart (5,87x1018 cm3molécula-1s -1). For the deuterated reactions, the total thermal rate constant CVT/SCT (1,65x10-15 cm3molécula-1s -1) is 3503 times greater than TST counterpart (4,71x10-19 cm3 molécula-1 s -1). The kinetic isotopic effect at this temperature, were 12, 38 (R1/R3) e 1, 41 (R2/R4) for the TST and 15, 23 (R1/R3) e 4, 94 (R2/R4) for CVT/SCT approximation.