The indirect through-space F–F coupling in peri-difluoronaphthalene: is it anisotropic?

Abstract

The ¹H, ¹⁹F and ¹³C spectra have been obtained of a sample of peri-difluoronaphthalene dissolved in the nematic liquid crystalline solvent ZLI 1695. The ¹³C satellite spectra from the six, single-¹³C isotopomers at natural abundance in both the ¹H and ¹⁹F spectra were identified and analysed to yield a set of residual total, anisotropic spin–spin couplings, T_ij. This was achieved by first obtaining residual ¹³C–¹⁹F and ¹³C–¹H couplings from a proton-encoded, ¹³C detected, local field 2D spectrum. The 45 values of T_HH, T_HF and T_CH were used to obtain the structure of the molecule, and then to estimate whether there is a significant contribution from the component along the magnetic field, J^aniso_ijzz, of the anisotropic, electron-mediated, spin–spin coupling tensors for ¹³C–¹⁹F and ¹⁹F–¹⁹F pairs. It is found that there is strong evidence for a significant contribution of J^aniso_FFzz to T_FF but not for the ¹³C–¹⁹F pairs.