High-Pressure-Limit and Pressure-Dependent Rate Rules for Intramolecular Cyclization Reactions of α,β -Hydroxyl Hydroperoxyalkyl Radicals

The cyclization reaction class of hydroxyl hydroperoxyalkyl radicals is one of the crucial reaction classes in low-temperature combustion mechanism of alcohols and alkenes. However, there is a lack of reports on accurate high-pressure-limit rate rules and pressure-dependent rate rules for this reaction class in literature. In this paper, 108 reactions are selected and divided into different classes according to the type of hydroxyl hydroperoxyalkyl radicals, the ring size of the transition states, and the position of the OH group. The energy barriers of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are calculated by the isodesmic reaction method, and the high-pressure-limit rate constants and pressure-dependent rate constants of all reactions are calculated using the TST and RRKM/ME theory, from which a high-pressure-limit rate rule and pressure-dependent rate rule for each subclass are established. It found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the calculated rate constants of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals are different from those of analogous reactions in alkanes, which indicates the necessity of establishing the rate rules for the cyclization reactions of hydroxyl hydroperoxyalkyl radical. There are large differences in energy barriers and rate constants among the whole reaction classes of the cyclization reactions of hydroxyl hydroperoxyalkyl radicals, so it is necessary to divide the cyclization reactions class into subclasses, and it is also shown that the pressure has a significant effect on the rate constants. In summary, accurate high-pressure-limit rate rules and pressure-dependent rate rules for the cyclization of hydroxyl hydroperoxyalkyl radicals have been developed in this study, which is helpful for the automatic construction of higher accuracy combustion mechanisms for alcohols and alkenes.