Thermodynamic properties and kinetic parameters of reactions involving O_2 ＋ substituted allylic radicals

摘要

Global warming and the depletion of fossil fuels have led to an increased interest in the use of biofuels as replacements for conventional gasoline and diesel transportation fuels. Such biofuels are often unsaturated, yet literature on the combustion kinetics of unsaturated molecules is scant. The presence of the double bond has the potential to impact the kinetics in several ways. For example, the weak allylic C-H bond could provide a low barrier pathway for RO_2 isomerization. However this pathway proceeds via a 7-membered transition state (including the double bond). Isomerization via the 6-membered transition state (a major pathway in alkyl peroxy systems) is significantly higher in energy since this involves abstraction of the stronger-bonded vinyllic C-H. There is also the potential for internal addition to the double bond. Using the CBS-QB3 method, combined with transition state theory, we calculated the high-pressure rate constants and thermochemistry of reactions involving methylallyl peroxy radicals. Pressure-dependent rate constants were calculated as a function of temperature and pressure for the various pathways of these chemically-activated systems.