Fluorine magnetic resonance studies. II. Long-range fluorine-fluorine coupling in 2,b,b-trifluorostyrenes and related compounds.

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 of conformational effects. The ultraviolet absorption spectra of the β,β difluorostyrenes are similar to those of the styrenes,