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 carbon yl oxide, H2COO, to HCO and OH radicals is unlikely in view of an acti vation enthalpy Delta Delta H-f(0)(298) of 31 kcal/mol. However, for d imethylcarbonyl oxide there is a low energy rearrangement mode(Delta D elta H-f(0)(298): 14.4 kcal/mol) which involves a H atom of the methyl group and which leads to a hydroperoxy methyl ethene intermediate, wh ich in turn can decompose to OH and CH2COCH3 radicals (Delta Delta H-f (0)(298): 23 kcal/mol), In the gas phase ozonolysis of alkyl substitut ed alkenes the formation of OH radicals is the most likely process. Th is has important consequences for the chemistry of the atmosphere.