Complete Assignment of ¹³C NMR Spectra and Determination of Orientational Order Parameter for Antiferroelectric Liquid-Crystalline MHPOBC

Abstract

Complete assignment of the 13C NMR lines is reported for both isotropic and oriented samples of antiferroelectric liquid-crystalline MHPOBC. Two-dimensional double-quantum coherence spectroscopy (2-D INADEQUATE) in the isotropic phase and field alignment-induced shifts (AIS) were studied. 19F−13C dipolar quartets were measured for TFMHPOBC, where a methyl group attached to the chiral center of MHPOBC is replaced by a trifluoromethyl group, to assist the assignment. Shielding tensor principal elements were determined for each carbon by site-separated spinning sideband spectroscopy (2-D TOSS-deTOSS). The orientational order parameter has been evaluated to be 0.73 at 403 K in the SA phase using the experimentally determined AIS and the tensor elements and assuming an intramolecular free rotation model.