The mechanism of methoxy radical oxidation: hydrogen abstraction versus trioxy radical formation

The energetic profiles of the two possible pathways of formaldehyde and HO₂ radical formation in the oxidation of the methoxy radical CH₃O, i.e. (a) via H-abstraction or (b) as addition/elimination involving methyl trioxy radicals CH₃OOO as intermediates, were calculated using G2M(RCC) and CBS-QCI/APNO model chemistries. The 298 K barrier height for path (a) is found to be 11.5 (14.8) kcal/mol at G2M(RCC) level (CBS-QCI/APNO value in parentheses). Along path (b), the HO₂ elimination from cis-CH₃OOO is found to have a barrier of 1.3 (8.5) kcal/mol. Therefore, oxidation of CH₃O is likely to occur by forming the CH₃OOO intermediate rather than by H-abstraction.