TEMPERATURE-DEPENDENT T-1 MEASUREMENTS OF C-13 AND N-14 IN ACETONITRILE DISSOLVED IN A THERMOTROPIC LIQUID-CRYSTAL

The methyl 13C and the 14N longitudinal relaxation times in acetonitrile, dissolved in a thermotropic liquid crystal, were studied as a function of temperature under the condition of proton decoupling. The 14N longitudinal relaxation time could be derived from the cyano 13C linewidth due to the incomplete averaging of the dipolar interactions in the nematic phase. The correlation times for the reorientation of the 13CH vector and for the reorientation about an axis perpendicular to the principal molecular axis were obtained using standard relaxation theory, with allowance for the ordering in the nematic phase and applying extreme narrowing arguments. The results strongly indicate that the equations derived for the isotropic phase, assuming rotational diffusion, cannot be applied to a molecule dissolved in a nematic phase merely by taking into account the partial orientation. © 1979.