NATURAL-ABUNDANCE H-2 NMR FOR LIQUID-CRYSTAL STUDIES - APPLICATION TO4'-(HEXYLOXY)-4-CYANOBIPHENYL

Quadrupolar splitting In deuterium NMR (H-2 NMR) is a powerful means t o evaluate microscopic orientational orders of liquid crystals. So far , because of the low sensitivity of H-2 NMR at natural abundance, appl ication of H-2 NMR to liquid crystals has been considered possible onl y for samples with deuterium enrichment. However, in the present work, we show that by taking advantage of the high sensitivity of a recent high-field NMR spectrometer, detection of H-2 NMR signals al the natur al abundance of the H-2 isotope is possible under proton decoupling, A ssignments of the H-2 NMR signals to specific chemical groups in the m olecule may be made by comparing H-2 chemical shift in the liquid crys talline phase with those of H-1 chemical shift in the isotropic phase, Subsequent evaluation of quadrupolar splittings gives microscopic ori entational orders of the molecule, With this technique, temperature de pendence of microscopic orders of 4'-(hexyloxy)-4-cyanobiphenyl is dem onstrated.