NUCLEAR MAGNETIC RESONANCE OF ORIENTED QUADRUPOLAR NUCLEI IN LIQUID CRYSTAL PHASES

Studies of quadrupolar nuclei in a number of liquid crystal pases are described, with the intent of determining quadrupole coupling constants or using the quadrupolar nuclei as probes of the structure and dynamics of liquid crystal phases.; Quadrupole coupling constants for the N-14 nucleus in methyl isocyanide and methyl ammonium ion were determined through observation of the proton and nitrogen resonances of these species dissolved in nematic phases. The results for the methyl isocyanide confirm earlier work that the quadrupole coupling constant of N-14 is abnormally lower than the values obtained from gas microwave studies. The quadrupole coupling constant of N-14 in methyl ammonium ion dissolved in a lyotropic phase is also significantly larger than that observed in methyl ammonium chloride crystals using double resonance NQR.; Deuterchloroform is used as a probe in studying the structure and dynamics in smectic phases. Emphasis is placed on the use of rotation of the smectic sample from the initial orientation. At sufficiently low concentrations of the solute probe molecule, rotation studies show that the solute is biaxially ordered. It is also observed that over a range of concentrations and temperatures, the solute takes on a number of distinct orientations. A preliminary investigation of the spin lattice relaxation rates of CDCl(,3) in the smectic phase has revealed a dependence on the angle of the liquid crystal director with respect to the magnetic field direction. Due to the high viscosity of the smectic phase studied, this angular dependence is ascribed to the rotational browian motion of the solute. The effect observed was small due to the weak ordering of the solute. Inhomogeneous broadening of the quadrupolar doublet made accurate measurements over the entire range of 0(DEGREES)-90(DEGREES) difficult and complete rotation studies will require very uniform director orientations.; Intermolecular contributions to the chemical shielding in crystalline benzene are also investigated through a comparison of solid state and liquid crystal measurements of the shielding anisotropy of benzene. A semiclassical ring current calculation applied to the benzene crystal lattice predicts a neighbor contribution to the anisotropy that brings the solid and liquid crystal measurements into accord. Possible intermolecular effects in the liquid crystal method are also experimentally tested.