Theoretical Study on Reactions of α-Site Hydroxyethyl and Hydroxypropyl Radicals with O2.

α-Site alcohol radicals are the most important products of H-abstract reactions from alcohols since the hydroxyl moiety weakens the α-site C-H bond. Reactions between α-site alcohol radicals and O2 play an important role in combustion of alcohols, especially at relatively low temperatures. However, reliable reaction pathways and rate constants for these reactions are still lacking. Theoretical studies on reactions in α-hydroxyethyl radical (CH3C•HOH) + O2 and α-hydroxypropyl radical (C2H5C•HOH and CH3C•OHCH3) + O2 reaction systems are performed in this work. Pressure-dependent rate constants for the involved reactions in a wide range of temperatures are determined using the Rice-Ramsperger-Kassel-Marcus/master equation (RRKM/ME) method. Our results show that rate constants for reactions in the α-hydroxypropyl radical + O2 system are quite different from those in the CH3C•HOH + O2 system. Detailed reaction pathways for these reaction systems are clarified, although combustion characteristics of ethanol and propanol do not change much with the obtained rate constants for these reactions. Important reaction channels in producing enols, especially in the combustion of propanol, are also provided. The obtained rate constants for these reactions over a wide range of temperatures and pressures are helpful in developing combustion mechanisms for ethanol and propanol.