Estimation of carbon-13 chemical shift anisotropy from aligned phase parameters in liquid crystals

An experimental approach for estimating carbon chemical shift anisotropy (CSA) of liquid crystals is demonstrated. The alignment-induced chemical shift (AIS) along with local order parameters calculated from dipolar couplings are utilized to determine CSA parameters of a particular carbon of interest. The experiment is carried out as a function of temperature so that reliable values are obtained and the best fit to data at all temperatures will increase the accuracy of the approach. The molecular orientational order information at different temperatures can be obtained from CSA values from the single 1D spectrum in a straightforward way from the AIS values. The advantage of this approach is that due to variations in the local order and the orientation of the CSA tensor with respect to the magnetic field, the spectra show wide dispersion of resonance frequencies, thereby avoiding the problem of overlap of spectral lines which is encountered generally in the solid state.