Proton Chemical-Shift Tensors of Methyl Groups; a Multiple-Pulse NMR and LORG/IGLOab InitioStudy
✍ Scribed by B. Tesche; U. Haeberlen
- Book ID
- 102595149
- Publisher
- Elsevier Science
- Year
- 1995
- Tongue
- English
- Weight
- 142 KB
- Volume
- 117
- Category
- Article
- ISSN
- 1064-1858
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✦ Synopsis
High-resolution proton spectra of single crystals of dimethyl ried out by Jackowski for acetonitrile, NC-CH 3 (5). If it is terephthalate (DMT) and rotation patterns of line shifts are revalid, the chemical-shift tensor of the protons in a methyl ported. The suppression of the proton-proton dipole-dipole intergroup, motionally averaged over the latter's omnipresent actions by multiple-pulse cycles works sufficiently well to achieve C 3 reorientations at ambient temperature, should as well be linewidths of less than 0.5 ppm and to follow the angular depenaxially symmetric with an anisotropy of dence of the chemical shifts of all 12 inequivalent protons in DMT in the rotation patterns. In this paper, the data from the methyl
groups are analyzed. The anisotropy of the methyl proton chemical-shift (CS) tensor is /(2.9 { 0.1) ppm. The asymmetry h is 0.25. LORG and IGLO ab initio CS calculations for the methyl where U is the angle subtended by the C 3 axis of the methyl ester fragment of DMT, supplemented by a hydrogen, i.e., for group and any of its C{H bond directions. If U equals the methyl formate, are also presented. Calculated and measured tetrahedral angle, 109.47Њ, Eq. [1] predicts that methyl proton CS tensors agree on the {0.5 ppm accuracy level. The calculated CS tensor of the C-H proton in methyl formate is compared with the intramolecular part of the previously mea-Ds methyl Å 0 1 3 Ds m .
[2]
sured CS tensors in calcium and lead formate. Again, remarkable agreement is found between calculated and measured proton CS tensors.