Fluorine magnetic resonance studies. II* Long-range fluorine-fluorine coupling in 2, β, β-Trifluorostyrenes and related compounds

Abstract

Five β, β-difluorostyrenes and a 1-difluoromethyleneindan bearing a fluorine substituent on the aromatic ring ortho to the side chain have been prepared from the corresponding carbonyl compounds. Sodium chlorodifluoroacetate and tris(dimethylamino)phosphine in triglyme at 160° is most effective in converting hindered ketones into β, β-difluorostyrenes. The 19F N.M.R. spectra for solutions of these compounds in carbon tetrachloride and dimethylformamide have been analysed. Fluorine-fluorine coupling over five bonds ranges from 4 Hz in the flexible 2, β, β-trifluorostyrene to 69 Hz in the rigid indan. Variations in the spectra produced by structural and solvent changes are explained in terms o..