A new approach is presented for the determination of long-range dipolar couplings in liquid crystals. The strategy is the use of monodeuterated compounds to observe 2H−13C splittings in the 13C NMR spectra. As examples, the H−C dipolar coupling constants have been obtained from the spectra of 4‘-cyanobiphenyl 2-deutero- and 6-deuterohexanoate over the whole nematic range. In addition, the 2H NMR spectra of these compounds taken with 1H−H dipolar decoupling show quadrupolar splitting and 1H−H dipolar coupling. Besides the information obtained from the 1D spectra, one-bond and two-bond 1H−13C dipolar coupling constants of 4‘-cyanobiphenyl hexanoate were determined using the method of proton encoded local field (PELF) spectroscopy in combination with off-magic-angle spinning (OMAS). The order parameters were calculated from the 2D spectra, and some of the coupling constants are compared with the H−C coupling constants obtained from the 1D experiments.

No abstract