Theoretical study on the kinetics and thermodynamics of H-atom abstractions from tetramethylsilane-related species

Theoretical kinetics and thermochemistry investigations on the H-atom abstraction reactions by H and O atoms and OH and HO₂ radicals from Si−C−O-containing species such as Si(CH₃)₄, Si(CH₃)₃(OH), Si(CH₃)₂(OH)₂, and Si(CH₃)(OH)₃ have been carried out in this work. The geometry, vibrational frequencies, and hindrance potential for each species are calculated at the B3LYP/6-31G(2df,p) level of theory with the single-point energies calculated at the G4 level of theory. The composite methods G3 and G4 are utilized to derive enthalpies of formation at 0 K by the atomization reaction methodology. ΔH_f(298 K), S(298 K), and C_p(T) are calculated by using the statistical thermodynamics method. Conventional transition state theory is used over a wide temperature range (298.15−2000 K) for H-atom abstraction reactions by H, O, and HO₂ radicals from the species mentioned above, and variational transition state theory is used for H-atom abstraction reactions by the OH radical. The kinetic and thermodynamic parameters based on high-level theoretical calculations are compared with the literature data. Reactivity comparison between the similar hydrocarbons and silicon-organic compounds for H-atom abstractions is explored. A large difference exists between these two different systems when H-atom abstractions are on hydroxyl sites.