Theoretical Determination of Enthalpies of Formation of Benzyloxy, Benzylperoxy, Hydroxyphenyl Radicals and Related Species in the Reaction of Toluene with the Hydroxyl Radical

Abstract

Reaction of toluene (T) with HO• produces addition products and the benzyl radical (TR). TR can react with HO • or O2 to produce oxygenated species, for many of which there is no experimental information. We present here theoretically determined heats of formation (HFs) of 17 such species using non-isodesmic reactions of TR+O2 and T+HO • +O2. For experimentally known HFs, we obtained a reasonable correlation between experimental and theoretical data for G4 (r2=0.999) and M06/cc-pVQZ (r2=0.997) results. Previously unknown HFs of other radicals (benzyloxy, spiro [1,2-dioxetane benzyl], hydroxyphenyl, and benzylperoxy) and closed shell species (salicylic alcohol, benzo [b]oxetane and p-hydroxy cyclohexa-2,5-dienone) were calculated using these methods. The species studied and the enthalpies of formation obtained were: salycilic alcohol, -69.7 ± 3.4 kcal/mol; benzyloxy radical, 28.4 ± 3.4 kcal/mol; hydroxyphenyl radical, 37.3 ± 3.4 kcal/mol; benzo [b]oxetane, 23.7 ± 3.4 kcal/mol; spiro [1,2-oxoetane phenyl] radical, 57.3 ± 3.4 kcal/mol; p-hydroxy cyclohexan-2,5-dienone, -42.1 ± 3.4 kcal/mol; and benzylperoxy radical, 28.5 ± 3.2 kcal/mol.