“…Furthermore, Weber et al 33 and Narayanaswamy et al 34 found that this reaction class is one of the most sensitive in promoting methylcyclohexane (MCH) autoignition at the intermediate temperature of approximately 900 K. Similarly, this was also observed in our recent study of n-propyl cyclohexane (nPCH) autoignition through a sensitivity analysis at 950 K, where this reaction class increases overall reactivity and promotes ignition. 35 However, the rate constants of this reaction class adopted in cycloalkane models are still based on the rate constant rules of acyclic alkanes. [36][37][38] In the current work, accurate rate constants for a series of reactions of H : O 2 radical with methyl cyclohexane (MCH), ethyl cyclohexane (ECH), n-propyl cyclohexane (nPCH), iso-propyl cyclohexane (iPCH), sec-butyl cyclohexane (sBCH), and iso-butyl cyclohexane (iBCH) were systematically calculated by combing highlevel ab initio calculations and conventional transition state theory.…”