Trigonal-13C hyperfine coupling in CF3CCl2

An intense isotropic ESR spectrum of CF3CCl2 is generated by annealing γ-irradiated samples of CF2CCl3 above 145 K, the sudden spectral change being irreversible and probably corresponding to the loss of a chloride ion from the CF3CCl3- radical anion. Satellite lines detected at high gain are assigned to CF313CCl2 with a 13C hyperfine coupling of 67.3 G, showing that th radical possesses a more planar configuration than that of the CCl3 radical (13C hfcapprox. =116 G). This result strongly supports a previous argument that increasing the electronegativity of the α substituent is much less important than the effect of π-conjugative destabilization in promoting the pyramidality of alkyl radicals