Electron spin resonance spectra and structure of the α,α-difluoroethyl radical

Abstract

Exposure of solid CH₃CF₂Cl and solid solutions of CH₃CF₂Cl in some organic solvents to ⁶⁰Co γ-rays at 77 K gives anisotropic e.s.r. spectra of CH₃ĊF₂ radicals. Using the spectra it has been shown that the internal rotation of the CH₃ group is greatly hindered at 77 K and that the hyperfine splitting of only one of the hydrogens in the CH₃ group is observed, reflecting a dihedral angle of 0^° between the C—H bond and the half-filled orbital at the C_α atom. The anisotropic spectra are in excellent agreement with a simulation spectrum which was made for a pyramidal structure very similar to that optimized by INDO calculations. On annealing of the irradiated solid CH₃CF₂Cl the spectrum of the CH₃ĊF₂ radical changed irreversibly at ca. 100 K, indicating the presence of a high-temperature form of the CH₃ĊF₂ radical. The e.s.r. spectrum for the high-temperature species has been satisfactorily interpreted on the assumption that the radical is undergoing libration about the axis passing through the mid-point of the two F atoms and that of the two C atoms of the pyramidal CH₃ĊF₂ radical.