Theoretical and Kinetic Study on the H-Atom Abstraction Reactions of 2-Methoxypyridine by Key Combustion Species

Abstract Combustion kinetics of nitrogen-containing heterocyclic compounds are important for understanding fuel-nitrogen conversion and NOx formation. Here, 2-methoxypyridine (2-MeOPy, C6H7NO) was selected as an oxygen- and nitrogen-containing heteroaromatic model compound to investigate H-abstraction from the methoxy side chain by key combustion species (H, CH3, OH, HO2, O, NH2, NO2, CH3O, and O2). Temperature- and pressure-dependent rate coefficients were calculated using CCSD(T)-F12a/cc-pVTZ-F12//M06-2X/6–311++G(d,p) electronic-structure calculations combined with variational transition-state theory and RRKM/master-equation calculations within the EStokTP framework. Pyridine nitrogen lowers the methoxy C–H bond dissociation energy from 103.38 kcal·mol–1 in anisole to 97.78 kcal·mol–1 in 2-MeOPy, but the kinetic response remains strongly species-dependent. The calculated rate coefficients exhibit different responses to nitrogen substitution among the investigated abstracting species, including temperature-dependent crossovers for H- and O-initiated abstraction. The OH channel forms a hydrogen-bonded pre-reactive complex, which is associated with low-temperature curvature and an apparent negative fitted Ea. These results provide species-specific kinetic parameters for the development of detailed combustion kinetic models for nitrogen-containing fuels.