Complete assignment of C-13 NMR spectra and determination of orientationalorder parameter for antiferroelectric liquid-crystalline MHPOBC

Complete assignment of the C-13 NMR lines is reported for both isotropic an d oriented samples of antiferroelectric liquid-crystalline MHPOBC. Two-dime nsional double-quantum coherence spectroscopy (2-D INADEQUATE) in the isotr opic phase and field alignment-induced shifts (AIS) were studied. F-19-C-13 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 S-A phase using the experimentally determined AIS and the ten sor elements and assuming an intramolecular free rotation model.