NMR investigations with liquid crystals are being used to study weak molecular interactions and to provide information on the degree of ordering of molecules dissolved in a liquid cyrstal solvent. Samples have been studied in nematic solvents while being spun at the """"""""magic angle"""""""". With natural abundance carbon-13 NMR, the relative intensities of the spinning sidebands have been shown to provide information on the sign of the order parameter at each carbon atom in the molecule. We are continuing to explore the mechanism and potential applications of the effect of isotopic substitution on NMR chemical shifts of nuclei that are several bonds away from the site of substitution. Studies of a number of differently substituted binuclear aromatic molecules (including cis- and trans-stilbenes, trans-azobenzene, diphenyl-acetylene and diphenylethane) were previously reported to show isotope-induced changes in carbon-13 chemical chifts through as many as 10 chemical bonds and as small as 0.64 parts per billion. The relation of the observations to details of molecular structure is being evaluated.
