A general strategy for obtaining 19F–19F and 13C–19F residual dipolar couplings in perfluorocarbons from the NMR spectroscopy of liquid crystalline samples

Abstract

A two-dimensional Fluorine Detected Local Field (FDLF) NMR experiment is demonstrated on a sample of perfluoropropyl iodide dissolved in the nematic solvent ZLI1132. In analogy to the proton detected local field (PDLF) technique, for each resolved site of the carbon spectrum, a simple map of the heteronuclear coupling network is obtained in the indirect dimension. A full analysis of the FDLF spectrum was achieved with the aid of two-dimensional ¹⁹F–¹³C HETCOR and ¹³C, D-resolved spectra (with D representing the anisotropic spin–spin coupling). A one-dimensional ¹⁹F spectrum was recorded on the same sample at intermediate resolution, and values of the residual spin–spin couplings T_CF and T_FF obtained from both experiments were combined and used to provide starting parameters for the analysis of a very high resolution ¹⁹F spectrum, including the weak satellite lines from single-¹³C isotopomers. The high-precision, residual, anisotropic couplings were used to explore whether they have an appreciable contribution from the anisotropic electron-mediated spin–spin couplings.