Determination of long-range dipolar couplings using mono-deuterated liquidcrystals

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