Proton shielding tensor, measurement

We think that the main reason for this decline of interest is the limited analytical value of proton shielding tensors. Even if one has the necessary equipment (few people have it) and the necessary know-how, it takes a considerable effort to actually measure a proton shielding tensor. For analytical purposes, the combination of line-narrowing m.p. sequences with magic angle sample spinning (CRAMPS) applied to a powder sample will usually be the method of choice (Scheler et al., 1976 Burum et al., 1993 for a recent review, see Maciel et al., 1990). However, the combination... 

The m.p. line-narrowing technique has added an impressively long list of proton shielding tensors a to our knowledge of material properties. Complementary access to such tensors is to calculate them by quantum chemical methods. An important advantage of this approach is that, in addition to the symmetric constituent of a, it also yields the components of the antisymmetric constituent o " that are virtually inaccessible to measurements by spectroscopic means. So far only relaxation studies have provided experimental information about (Kuhn, 1983 Anet and O Leary, 1992). Note that these experiments were done on carbons. 

Tjandra N, Bax A (1997) Solution NMR measurement of amide proton chemical shift anisotropy in N-ebmiched proteins. Corrrelation with hydrogen bond length. J Am Chem Soc 119 8076-8082 Tossell JA (1984) Correlation of Si NMR chemical shifts in sihcates with orbital energy differences obtained from x-ray spectra. Phys Chem Mineral 10 137-141 Tossell JA (1992) Calculation of the Si NMR shielding tensor in forsterite. Phys Chem Mineral 19 338-342... 

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