Quadrupole Splittings in Liquid Crystals

Abstract

It has already been emphasized above that the NMR characteristics of chlorine, bromine and iodine nuclei are to a great extent determined by their large quadrupole moments which couple with inhomogeneous electric fields. In those cases considered so far it has been tacitly implied that the molecular environment is isotropic, i.e. that all directions of the electric field gradient with respect to the external magnetic field are equally probable. However, even a slight anisotropy may considerably perturb the spectrum from its normal single Lorentzian curve into a more complex pattern, which is analogous to that observed for solids. Let us first discuss briefly the shape of the spectra obtained for quadrupolar nuclei in solids [23] and then outline the treatment relevant to NMR of anisotropic fluid systems such as for example liquid crystals.