A comparison of proton‐detected 13C local field experiments with deuterium NMR at natural abundance for studying liquid crystals

Abstract

A comparison is made between the information which can be derived on structure, conformation and orientational order of the molecules in a nematic liquid crystal 4‐pentyl‐4′‐cyanobiphenyl (5CB) from the NMR spectra of the deuterium atoms at natural abundance (NAD NMR), and the two‐dimensional proton‐detected 13C local field experiment (PDLF). The nine residual quadrupolar splittings, Δν k , obtained experimentally have been compared with quadrupolar tensors and a geometry and conformational potentials calculated by the DFT method B3LYP/6‐311G**. The PDLF experiment yielded 42 scaled 13C–1H residual dipolar couplings, kD CiHj . The scaling factor, k, is determined experimentally by comparing unscaled and scaled residual dipolar couplings in a sample of fluorobenzene dissolved in a nematic liquid crystalline solvent. The corrected residual dipolar couplings, D CiHj , are used to investigate the structure and rotational potentials about each bond in the molecule.