13C MAS NMR Spectra ofcis,cis-Mucononitrile in Liquid-Crystalline Media and in the Solid State. Orientation of the Carbon Chemical-Shift Tensors

✍ Scribed by K.V. Ramanathan; N. Suryaprakash; C.L. Khetrapal; Edwin D. Becker; Klaus Eichele; Roderick E. Wasylishen

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 128 KB
• Volume: 123
• Category: Article
• ISSN: 1064-1858
• DOI: 10.1006/jmra.1996.0235

✦ Synopsis

The spinning sidebands observed in the 13 C MAS NMR spectra (Fig. 1a), oriented in a nematic phase and in the solid state of cis,cis-mucononitrile oriented in liquid-crystalline media and of are presented. As a consequence of the carbon-13 chemicalthe neat sample in the solid state are studied. There are differences shift anisotropy (CSA), spinning sidebands are observed in in the sideband intensity patterns in the two cases. These differboth liquid-crystal and solid-state NMR spectra. Differences ences arise because the order parameters which characterize the in the relative sideband intensities between these experiorientation of the solute in the liquid-crystalline media differ for ments arise from the fact that in the liquid-crystalline phase different axes. It is shown that, in general, the relative intensities ordering along the different molecular axes is different. It of the sidebands contain information on the sign and magnitude is demonstrated that knowledge of the ordering matrix of of an effective chemical-shift parameter which is a function of the the system can be used to determine the orientation of the sum of the products of the principal components of the chemicalprincipal axes of the chemical-shift tensor in the molecular shift tensor and the corresponding order parameters with respect to the director. A method for obtaining the orientation of the frame of reference. In general, such information is unavailcarbon chemical-shift tensor is proposed. The carbon chemicalable from solid-state NMR studies of powder samples (5).

shift tensors obtained from gauge-including atomic orbital calculations are also presented for comparison.