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

The through-space NMR spin-spin coupling mechanism between F-19 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 1p(sigma) and 1p(sigma)-1p(sigma) contributions to the FC term are larger than the corresponding 1p(pi(ip)) contributions. The passive 1p(pi) 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 sigma through-bond coupling (-19 Hz). The magnitude of through-space coupling can be predicted with a suitable model. (C) 2004 Elsevier B.V. All rights reserved.