The 19F NMR spectra of the cis- ( 1 ) and the trans-isomer ( 2 ) of the 1,2-dichlorotetrafluorocyclopropane and that of the 1,1-dichlorotetrafluorocyclopropane ( 3 ) have been investigated at different temperatures and in several solvents. From chemical shift calculations the two geminal fluorines in the cis-isomer ( 1 ) could be assigned and on this basis the two vicinal coupling constants of 1 , Jtrans (ca. 140°) and Jcis (ca. 0°), were unequivocally distinguished. By frequency sweep double resonance Jtrans has been shown to be of opposite sign to Jgem, whereas for Jcis the situation has been found to be reversed. Therefore Jtrans is presumably negative and Jcis positive. Only the N(Jcis + Jtrans) value could be extracted from the vicinal coupling constant in the fragment ? CFCl? CFCl? could be evaluated. It has been noted that Jcis is more sensitive to changes in temperature than is Jtrans. The variations of Jcis and Jtrans induced by solvents are, on the contrary, small and irregular and no correlation with the dielectric constant of the medium has been noted. The different temperature dependence of Jcis and Jtrans can be useful for assigning the vicinal F? F coupling constants in cyclopropane derivatives and also for defining their signs. This method was applied to the coupling constants extracted from the 13C satellite spectrum of isomer 3 . The coupling constants results were compared with some literature data already known, and some rationalisation and correlations from the trends was attempted.
