Orientation and Structure of Pyrazine, Pyrimidine, and Pyridazine in a Lyotropic Liquid Crystal

Abstract

High resolution proton magnetic resonance spectra of pyrazine, pyrimidine, and pyridazine partially oriented in a lyotropic mesophase have been obtained and analyzed. The distance ratios calculated from the direct dipole-dipole couplings are compared with those reported for microwave and X-ray studies in the gaseous and solid state as well as those determined from NMR investigations of the above solutes in thermotropic nematic phases. The average orientation of the diazines in the oriented lyotropic phase is such that the applied magnetic field is parallel to the molecular plane. In contrast, the average orientation of benzene, furan, thiophene, p-dithiin, and tetrafluoro-1,3-dithietane is such that the molecular ring is on the average perpendicular to the applied magnetic field. Sine benzene, furan, thiophene, and the diazines orient with the molecular plane parallel to the magnetic field in thermotropic nematic phases, contributions from different orienting factors appear to be operative in the lyotropic phase.