Hyperfine coupling constants and angles of twist of phenyl and pentafluorophenyl substituted methyl radicals

Abstract

The ring proton hyperfine coupling constants of the benzyl, diphenylmethyl and triphenylmethyl radicals are compared with fluorine splittings in the corresponding perfluorophenyl radicals. Trends in the ratio of a_F/a_H are rationalised in terms of twisting of the phenyl rings; INDO calculations on model systems support this interpretation and suggest that a comparison of ring proton and fluorine hyperfine interactions, particularly at the meta positions, can provide useful stereochemical information.