NMR METHODS TO MEASURE CHEMICAL SHIFT ANISOTROPY 3.1 Introduction Cross-Polarisation-magic-angle-spinning (CPMAS) with high-power proton decoupling

Cross-Polarisation-magic-angle-spinning (CPMAS) with high-power proton decoupling [Schaefer, 1976] has been widely applied to obtain high resolution NMR spectra of dilute spin1/2 in solids. This method averages out all anisotropic NMR interactions which transform as second-rank tensors, such as chemical shift anisotropical interactions. However, the principal elements of chemical shift anisotropy tensor contain useful information on structure, dynamics and orientation of molecular segments. Attempts to recover these CSA parameters in high resolution solid-state NMR appeared almost at the same time with the introduction of CPMAS technique [Lipmaa, 1976; Stejskal, 1977].