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Abstract:
By computer fitting of resonance lines in deuteron spectra of perdeuterated crystals, deuteron chemical shifts in crystals are measured with an accuracy of ±0.3 ppm. Second-order quadrupole shifts must be taken into account. An important advantage of the method is that the measured chemical shifts and the shift tensors are automatically related to EFG tensors which can be assigned easily. The method is applied to α-glycine for which a shift anisotropy Δσ = 21 ± 9 ppm has been reported for the methylene protons. Full EFG and chemical-shift tensors are reported at both methylene deuteron sites, and motionally averaged tensors are reported for the ND3+ sites. The shift anisotropies Δσ for the methylene deuterons are 4.7 and 9.4 ppm, respectively. Significant differences of the isotropic shifts and quadrupole coupling constants are also observed for these two deuterons. They are interpreted as evidence for the formation of a weak CH … O hydrogen bond in α-glycine.
