Quantum chemical estimation of the possibility of the formation of chloro- and bromomethane radical anions and their fragmentation paths in the gas phase and in solution by MNDO and AM1 techniques

By semiempirical MNDO and AM1 methods it was shown that electron transfer on the chloro-and bromomethane molecules of the general formula CH_nHal_4–n (n=1–3) results either in a kinetically independent particle, i.e., a radical anion, or in C-Hal-bond cleavage with the formation of Hal^– and the respective radical. The enthalpy, activation energy of the reactions, and data on the geometry of the radical anion obtained show that the increasing the number of halogen atoms in the initial molecule and decreasing the solvent polarity favor radical anion stabilization. It was established that the cleavage of the C-H-bond in the radical anion is not favored energetically. Fragmentation at the C-H-bond can proceed according to the mechanism of dissociative electron capture by halomethane molecule only with additional factors favoring this reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1886–1892, November, 1993.