NMR Studies of Some Liquid Crystal Systems

Abstract

Alignment by electric or magnetic fields of molecules comprising the liquid crystalline phase of a nematogenic material is manifested in proton magnetic resonance spectroscopy by the appearance of nuclear dipole‐dipole fine structure. Additionally, much larger splittings ranging up to 300 G are observed in the deuterium magnetic resonance spectrum of deuterium substituted nematogens. These latter splittings arise from perturbation of the Zeeman levels by the quadrupole coupling constant of deuterium and have been of value in elucidating structure and organization in nematic phases. Results of NMR studies on nematogens based on azoxy and carboxylic compounds are presented. Use of nematic phases as ordering matrices for molecules such as benzene, toluene, naphthalene, and stilbene are discussed. Some preliminary results on effects of electric fields and dissolved cholesteryl acetate on orientation and organization of nematogens also are presented. In addition, quadrupole coupling constants for deuterium bound to sp² and sp³ carbon and for deuterium bound to oxygen in a carboxylic acid dimer were determined for a few selected compounds.