Vibration-rotation coupling in anisotropic environments. II. Quadrupolar couplings of methanes in liquid crystals

It is shown that deuterium quadrupolar couplings observed when the deuterated methanes are dissolved in liquid crystals can be understood on the basis of the same vibration-rotation coupling mechanism which can explain the measured dipolar couplings. Two quantitites are obtained from the analysis: (i) the electric field gradient at the site of the deuterium nucleus when the deuterated methane possesses its equilibrium geometry; and (ii) the derivative of this field gradient with respect to the F2 stretch symmetry mode, taken at the equilibrium geometry. In order to obtain consistency, the presence of an external electric field gradient in the liquid–crystal solvent is required and its magnitude is estimated.