Rigid-Lattice NMR Moments and Line Shapes with Chemical-Shift Anisotropy

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Abstract
The effects of anisotropic chemical shifts upon high‐field, rigid‐lattice NMR lines are investigated for cases in which both direct and indirect dipolar interactions are present. The feasibility criteria for experimentally determining anisotropic chemical‐shift information in the presence of somewhat greater dipolar perturbations are examined. In doing so, the usual second‐moment method is discussed with respect to obtaining the magnitude of the chemical‐shift anisotropy. In addition, a general expression for the third moment is derived, and it is found that this parameter may be useful in determining the sign of the chemical‐shift anisotropy. Finally, theoretical line shapes are calculated for polycrystalline, two‐spin systems assuming axial symmetry at the nucleus being observed and including the anisotropic chemical shift, direct, and indirect dipolar interactions.