C-13 MAS NMR-SPECTRA OF CIS,CIS-MUCONONITRILE IN LIQUID-CRYSTALLINE MEDIA AND IN THE SOLID-STATE - ORIENTATION OF THE CARBON CHEMICAL-SHIFTTENSORS

The spinning sidebands observed in the C-13 MAS NMR spectra of cis,cis -mucononitrile oriented in liquid-crystalline media and of the neat sa mple in the solid state are studied. There are differences in the side band intensity patterns in the two cases. These differences arise beca use the order parameters which characterize the orientation of the sol ute in the liquid-crystalline media differ for different axes. It is s hown that, in general, the relative intensities of the sidebands conta in information on the sign and magnitude of an effective chemical-shif t parameter which is a function of the sum of the products of the prin cipal components of the chemical-shift tensor and the corresponding or der parameters with respect to the director. A method for obtaining th e orientation of the carbon chemical-shift tensor is proposed. The car bon chemical-shift tensors obtained from gauge-including atomic orbita l calculations are also presented for comparison. (C) 1996 Academic Pr ess, Inc.