Experimental Methods of Determining the Shielding Anisotropy

As noted in equation (8), the a components can be obtained directly from the moments of inertia, the internuclear distances, and the spin-rotation constants measured in a molecular beam experiment. These can be combined with accurate theoretical a components. Advantages of this method are that absolute shielding components are obtained, and are not subject to medium effects. Spin-rotational constants published prior to 1974 are summarized in Landolt-Bornstein tables. Some 

Shielding anisotropies can be obtained from measured relaxation times when the chemical shift anisotropy relaxation mechanism or the spin-rotation mechanism is dominant. The correlation time has to be estimated or otherwise derived. There are large uncertainties associated with this method. 

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