A positive “through-space” fluorine-fluorine coupling constant in perfluorotoluene

Abstract

All the fluorine chemical shifts and the signs and magnitudes of the fluorine-fluorine coupling constants of perfluorotoluene have been determined. The most important finding is that the large four-bond fluorine-fluorine coupling constant between an ortho-fluorine nucleus and the perfluoromethyl nuclei is positive. This means, that despite theoretical predictions to the contrary, all known fluorine-fluorine coupling constants containing a large “through-space” contribution are positive.