Theoretical Study of an Undisclosed Reaction Class: Direct H-Atom Abstraction from Allylic Radicals by Molecular Oxygen

The 1-methylallyl (C4H71-3) allylic radical is an important intermediate species in oxidation of linear C4 unsaturated hydrocarbons (1-butene, 2-butene, and 1,3-butadiene). This study reports the first high-level quantum chemical calculations for undisclosed reaction class this at to high temperatures: direct H-atom abstraction from terminal methyl group by molecular oxygen. Moreover, we systematically calculated rate constants primary, secondary, tertiary C4, C5, C6 radicals, respectively. Our results can be further used as rules kinetic model development hydrocarbon oxidation. All were implemented using two different ab initio solvers: Gaussian ORCA, three sets methods, MultiWell PAPR. Temperature dependent thermochemistry carried out based on transition state theory statistical thermodynamics, primary site found faster than that secondary sites C5 contrary common understanding. Barrier heights predicted solvers methods are about 4–5 kcal/mol different, which a factor 4–86 difference constant predictions depending temperature. Using solver with Method 2 most effective combination predicting accurate when compared against experimental data. When comparing solvers, both coefficients show good agreement wide range temperatures, except reactions (about 5–17 3–4 differences obtained, respectively). From application point view, incorporated calculation into AramcoMech2.0 model, systematic improvements ignition delay time, laminar flame speed speciation targets 2-butene