Analysis of the NMR through-space coupling mechanism between 19F atoms

The through-space NMR spin–spin coupling mechanism between 19F nuclei was investigated at the coupled perturbed density functional level using a BLYP(60:40) functional and a large basis set. Through-space coupling decays exponentially with the distance R(F,F) and is strongly angular dependent. The lp(σ) and lp(σ)–lp(σ) contributions to the FC term are larger than the corresponding lp(πip) contributions. The passive lp(π) contributions are responsible for 10% of the FC mechanism. The PSO term is not negligible. In 1,8-difluoronaphthalene, the FC term of 56 Hz results from through-space coupling (75 Hz) and σ through-bond coupling (−19 Hz). The magnitude of through-space coupling can be predicted with a suitable model.