Thermochemistry and kinetics of acetonylperoxy radical isomerisation and decomposition: a quantum chemistry and CVT/SCT approach

Abstract

CBS-QB3 calculations have been used to determine thermochemical and kinetic parameters of the isomerisation and decomposition reactions of the acetonylperoxy radical, CH₃C(O)CH₂OO˙, which has been formed via the reaction of acetonyl radical with O₂ leading to the formation of an energised peroxy adduct with a calculated well depth of near 111 kJ mol⁻¹. This species can undergo subsequent 1,5 and 1,3 H-shifts to give the primary and secondary radicals: C˙H₂C(O)CH₂OOH and CH₃C(O)C˙HOOH, respectively, or rearrange to give a 3-methyl-1,2-dioxetan-3-yloxy radical. Rate constants for isomerisation and subsequent decomposition have been estimated using canonical variational transition state theory with small curvature tunneling CVT/SCT. The variational effect for the isomerisation channels is only moderate but the tunneling correction is significant at temperatures up to 1000 K; the formation of a primary radical by a 1,5-shift is the main reaction channel and the competition with the secondary one starts only at around 1500 K. The fate of the primary acetonylhydroperoxy radical is predominantly to form oxetan-3-one while the ketene and 1-oxy-3-hydroxyacetonyl radical channels only compete with the formation of oxetan-3-one at temperatures >1200 K. In addition, consistent and reliable enthalpies of formation have been computed for the molecules acetonylhydroperoxide, 1,3-dihydroxyacetone, methylglyoxal and cyclobutanone, and for some related radicals.