Intramolecular H-Migration Kinetics of •OOQOOH Radicals for KHP Formation During Low-Temperature Oxidation of...

Alkylcyclohexanes are vital components of aviation kerosene. Intramolecular H-migration of •OOQOOH radicals controls ketohydroperoxide (KHP) formation, the primary pathway responsible for low-temperature chain-branching during low-temperature oxidation. Available chemical kinetic models for alkylcyclohexanes generally lack directly computed kinetic data for H-migration reactions of •OOQOOH in cyclic fuels; relevant rate constants are commonly transferred from analogous alkane reactions, introducing systematic uncertainties in low-temperature ignition predictions. In this work, quantum chemical calculations are performed for 13 representative •OOQOOH intramolecular H-migration pathways originating from alkylcyclohexanes, covering six structural subclasses: 1,5-H-(s)(p), 1,5-H-(s)(s), 1,5-H-(t)(p), 1,5-H-(t)(s), 1,6-H-(t)(p), and 1,6-H-(t)(s). Modified Arrhenius parameters are fitted from high-pressure-limit rate constants over 500-1500 K. Further comparison between the present computed rate data and parameters adopted in existing mechanisms demonstrates that the literature values transferred from alkanes are systematically lower. Ring strain and distinct transition-state entropy originating from cyclic structures make the alkane kinetic parameters inappropriate for alkylcyclohexane systems. The kinetic parameters and lumped subclass rate rules obtained in this study provide fundamental data for improving low-temperature oxidation models of alkylcyclohexanes.