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FF coupling constants in dichlorotetrafluorocyclopropanes
Author(s) -
Cavalli Luciano
Publication year - 1970
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270020303
Subject(s) - vicinal , geminal , chemistry , coupling constant , cis–trans isomerism , spectral line , nuclear magnetic resonance , stereochemistry , computational chemistry , physics , organic chemistry , quantum mechanics
The 19 F 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 , J trans ( ca. 140°) and J cis ( ca. 0°), were unequivocally distinguished. By frequency sweep double resonance J trans has been shown to be of opposite sign to J gem , whereas for J cis the situation has been found to be reversed. Therefore J trans is presumably negative and J cis positive. Only the N( J cis + J trans ) value could be extracted from the vicinal coupling constant in the fragment CFClCFCl could be evaluated. It has been noted that J cis is more sensitive to changes in temperature than is J trans . The variations of J cis and J trans 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 J cis and J trans can be useful for assigning the vicinal FF coupling constants in cyclopropane derivatives and also for defining their signs. This method was applied to the coupling constants extracted from the 13 C 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.