Hydrogen abstractions from methyl groups by atomic oxygen. Kinetic isotope effects calculated from MNDO/UHF results and an assessment of their applicability to monooxygenase-dependent hydroxylations

The semiempirical MNDO SCF-MO method has been applied to the calculation of kinetic isotope effects for methyl-hydrogen abstraction reactions involving O(/sup 3/P) and CH/sub 4/, propene, toluene, CHCl/sub 3/, and acetone. Transition states for these abstractions were characterized, and appropriate deuterium and tritium substitutions were made so as to permit comparisons of inter- and intramolecular isotope effects. A tunneling correction was used, and, while internal rotor corrections are discussed for propene, toluene, and acetone, they could not be fully applied due to the tendency of MNDO to underestimate internal rotation barriers. The applicability of isotope effects derived from this triplet oxene model to monooxygenase hydroxylation is discussed.