2H and 13C NMR studies of molecular orientation and dynamics in liquid crystal 6BA

The dynamics and orientation of dimers accompanying the formation and destruction of hydrogen bonds in the nematic phases of 4-n-hexylbenzoic acid (6BA) were studied by 13C and 2H NMR. The orientational order parameter S in the nematic phase was estimated from the quadrupole splitting of the 2H NMR spectrum. The intermolecular interaction energy for the molecular order in the nematic phase decreased with increasing temperature. The flexibility of dimers due to the destruction of the hydrogen bond is closely related to a decrease in the intermolecular interaction energy. The proportion of 2H NMR spin-lattice relaxation time (T1) to S, which reveals the coupling of the orientational fluctuations with the hydrogen bonding processes, was observed.