Analysis of Nuclear Magnetic Resonance Spectra of Molecules in Liquid-Crystal Solvents

Abstract

A convenient method to analyze the high-resolution nuclear magnetic resonance spectra of molecules dissolved in liquid-crystal solvents is described and related to basic theory of magnetic resonance. The method is applied to analyze the proton and fluorine NMR spectra of monofluorobenzene in a nematic liquid-crystal solvent. Parameters deduced from this analysis and describing the anisotropic molecular motion, the direct magnetic dipole—dipole interactions Dij, the indirect spin—spin couplings Jij, and the anisotropy of the diamagnetic shielding constant of F in the C–F bond are summarized and compared with the values for benzene and hexafluorobenzene in the same solvent. It is shown that agreement of experimental and computer-simulated theoretical spectra is probably limited by the accuracy of relative bond lengths in the assumed geometry for fluorobenzene. It is concluded that for many molecules having a large number (N≥3) of spin-½ nuclei, it is possible in the analysis of these spectra to reject incorrect hypothetical geometries and even to obtain refined relative positions for the magnetic nuclei.