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.