Theoretical kinetic investigation of thermal decomposition of methylcyclohexane

- H-atom abstraction reactions are energetically favored over other types of reactions.
- Alkyl radicals are easier isomerize to form resonance stabilized allylic radicals.
- The products of MCH thermal decomposition are some molecules like CH4, C2H4, etc.

The thermal decomposition of methylcyclohexane (MCH) has been investigated at the CBS-QB3 and CCSD level of theory. The pyrolysis of MCH follows a radical chain mechanism, which mainly includes the C-C bond scission, H-atom abstraction, secondary and biradical reactions. Thermodynamic data for selected species involved in this study are computed at the CBS-QB3 level. The rate constants for all elementary reactions are also evaluated with conventional transition state theory (TST) in the temperature range of 298-2000 K, where Eckart method is adopted to correct the quantum mechanical tunneling effect. The rate constants are reasonable agreement with experimental measurements and previous theoretical reports. Furthermore, the final products of MCH thermal decomposition are methane (CH4), ethylene (C2H4), propylene (C3H6), 1,3-butadiene (1,3-C4H6), isoprene (C5H8) and 1,3-pentadiene (1,3-C5H8). The main goal of this work is to give an exhaustive description of the MCH thermal decomposition by means of high level quantum chemical methods and provide a reliable reference for thermodynamic and kinetic information.

Five different kinds of H-atom abstraction barrier of MCH by CH3 radical is found to increase in the order of TS2 < TS3 ≈ TS4 ≈ TS5 < TS1, indicating that the tertiary H-atom abstraction channel is energetically favored over the primary and secondary channels.