Formation of OH radicals in the gas phase ozonolysis of alkenes: the unexpected role of carbonyl oxides

According to CCSD(T)/TZ + 2P calculations, the decomposition of carbonyl oxide, H ₂COO to HCO and OH radicals is unlikely in view of an activation enthalpy ΔΔH_f⁰(298) of 31 kcal/mol. However, for dimethylcarbonyl oxide there is a low energy rearrangement mode ( ΔΔH_f⁰(298): 14.4 kca/mol) which involves a H atom of ghe methyl group and which leads to a hydroperoxy methyl ethene intermediate, which in turn can decompose to OH and CH ₂COCH ₃ radicals ( ΔΔH_f⁰(298): 23 kcal/mol). In the gas phase ozonolysis of alkyl substituted alkenes the formation of OH radicals is the most likely process. This has important consequences for the chemistry of the atmosphere.