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An exhaustive and theoretical analysis for the CH3SCH3 + HOO• and CH3CH2SCH3 + HOO• reactions has been examined using quantum chemistry theory. The potential energy surface was obtained by the CCSD(T)/CBS//M06-2X/cc-pVTZ level of theory. The overall rate coefficients have been calculated and the energetics and reaction enthalpies are also calculated. The calculated kinetics demonstrate that the hydrogen abstraction channels from the -CH3 group in CH3SCH3 and the -CH2 group in CH3CH2SCH3 are major channels in the low temperature region (less than 1000 K). However, the CH3-transfer channels forming CH3OOH become competitive reaction channels with the increase in temperature.

Ab initio study of the reactions of n-heptyl radicals(1-C7H15, 2-C7H15, 3-C7H15, and 4-C7H15) with methanol was conducted over the temperature range of 300–1500 K. Transition states for the reaction channels producing C7H15OH, CH3, C7H15OCH3, H, C7H16, CH2OH and CH3O were identified and the geometries of all stationary points were calculated at BB1K/MG3S level of theory. The potential barrier heights of the corresponding transition states were predicted by the CBS-QB3//BB1K and G4//BB1K methods, indicating that the eight H-abstraction channels are more kinetically favorable than the channels where OH transfers from CH3OH to C7H15 and where the C7H15OCH3+H products are given. The rate constants of H-abstraction channels were calculated with TST and TST/Eck. Both the forward and reverse rate constants have positive temperature dependence and the tunneling effect is only important at the temperature lower than 700 K. For the reactions of H-atom abstraction from methyl in CH3OH by n-heptyl, a reverse and the corresponding forward rate constant are roughly equal. For the reactions of H-atom abstraction from OH in CH3OH by n-heptyl, a reverse rate constant is larger by several orders of magnitude than the corresponding forward one.