Nuclear spin-spin coupling via nonbonded interactions. 8. The distance dependence of through-space fluorine-Fluorine coupling

Article abstract of DOI:10.1021/ja993032z

The ¹⁹F¹⁹F nuclear spin-spin coupling constants J(FF) for a set of eighteen compounds related structurally to 1,8-difluoronaphthalene were measured by ¹⁹F NMR spectroscopy. The FF distances d(FF) in these compounds were determined by ab initio 3-21G* molecular orbital calculations. Consistent with the lone-pair overlap theory of the origins of through-space ¹⁹F¹⁹F coupling, an exponential relationship is found between J(FF) and d(FF) (regression coefficient r² = 0.991), and a linear relationship is found between J(FF) and the extent of the overlap interaction between the in- plane fluorine 2p lone-pair orbitals (regression coefficient r² = 0.993). The magnitudes of these lone-pair interactions were estimated from molecular orbital energies obtained by ab initio 6-31G* calculations for a model consisting of a pair of HF molecules separated by various distances.