Fluorine magnetic resonance studies. I. para-Substituted β,β-difluorostyrenes

A series of seven para-substituted β,β-difluorostyrenes has been prepared and their proton and fluorine magnetic resonance spectra recorded. The fluorine spectra show interesting correlations with the σ- values for the para substituents, the fluorine resonances moving to lower field and the geminal fluorine-fluorine coupling constant decreasing as σ- increases. These trends parallel those observed in the analogous styrenes but rather more precise relationships have been established for the fluorine compounds. Long range fluorine-fluorine spin-spin coupling over six and seven bonds, respectively, has been observed in the β,β,β,3- and β,β,4-trifluoro-styrenes.