NUCLEAR-SPIN SPIN COUPLING VIA NONBONDED INTERACTIONS .7. EFFECTS OF MOLECULAR-STRUCTURE ON N-F COUPLING

To test whether the recently discovered phenomenon of through-space nuclear spin-spin coupling between intramolecularly crowded N-15 and F-19 nuclei shows the same sort of striking dependence on molecular structure as the long-known phenomenon of through-space nuclear spin-spin coupling between pairs of intramolecularly crowded F-19 nuclei, several N-15-enriched oximes and some simple derivatives thereof were synthesized and their J(NF) values were determined by F-19 NMR spectroscopy. The experimental J(NF) values ranged from 8.6 to 43.5 Hz. The molecular structures of these compounds were determined by single-crystal X-ray diffraction. The observed dependence of the N-15-F-19 coupling constants on molecular structure was qualitatively consistent with the predictions of the lone-pair orbital overlap theory that was developed earlier to account for through-space coupling involving fluorine nuclei.