Rapid Hydrogen Shift Scrambling in Hydroperoxy-Substituted Organic Peroxy Radicals

Abstract

Using quantum mechanical calculations, we have investigated hydrogen shift (H-shift) reactions in peroxy radicals derived from the atmospheric oxidation of 1-pentene (CH_2═CHCH_2CH_2CH_3) and its monosubstituted derivatives. We investigate the peroxy radicals, HOCH_2CH(OO)CR_1HCH_2CH_3, HOCH_2CH(OO)CH_2CR_1HCH_3, and HOCH_2CH(OO)CH_2CH_2CR_1H_2, where the substituent R_1 is an alcoholic (OH), a hydroperoxy (OOH), or a methoxy (OCH_3) group. For peroxy radicals with an OOH substituent, the H-shift reaction from the hydrogen atom on the OOH group to the OO group is extremely fast. We find that the rate constants of this type of H-shift reactions are greater than 10^3 s^(–1) for both the forward and the reverse reactions. It leads to the formation of two different radical isomers that react through different reaction mechanisms and yield different products. These very fast H-shift reactions are much faster than the reactions with NO and HO_2 under most atmospheric conditions and must be included in the atmospheric modeling of volatile organic compounds where hydroperoxy peroxy radicals are formed.

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