Electron structure and reactivity of organofluorine compounds. 4. AMI calculations of anion radicals of primary, secondary, and tertiary perfluoroalkyl chlorides, bromides, and iodides

Abstract

Calculations were carried out using the semiempirical quantum chemical AMI method for anion radicals (AR) of the perfluoroalkyl halides (RFX): CF3X, CF3CF2X, (CF3)2-CFX, and (CF3)3CX for X=Cl, Br, and I. All the AR's studied are thermally stable. The electron affinity of the perfluoroalkyl halides, and consequently, the thermal stability of their AR's increases in the series from F-methyl to F-tertbutyl halides and from the chlorides to bromides and iodides. During formation of an AR the spin density is preferentially localized on the σ* orbital of the Cα−X bond which leads to an increase in the distance between these atoms. Dissociation of the AR of tert-perfluorobutyl iodide to a perfluorocarbanion and an I atom is thermodynamically more favorable than dissociation with formation of a perfluoroalkyl radical and I−.