Chemical-shift anisotropy line-shape effects

P line shapes have been used to study the motion of a phosphate ester in BPA-PC and in a blend of PS and PPO [753,754]. One-dimensional solid echo P chemical shift anisotropy line shapes are an effective means of determining rate and amplitude of ester motion. P Hahn echo spectra of 5 to 20 wt.% tris(2-ethylhexyl)phosphate (TEHP) in tetramethylpolycarbonate (TMBPA-PC) were the basis of a study of diluent dynamics [755]. 

Figure 3 Characteristic solid state NMR line shapes, dominated by the chemical shift anisotropy. The spatial distribution of the chemical shift is assumed to be spherically symmetric (a), axially symmetric (b), and completely asymmetric (c). The top trace shows theoretical line shapes, while the bottom trace shows rear spectra influenced by broadening effects due to dipole-dipole couplings.

The effect of magic-angle spinning on the C NMR spectra of oil shales is shown in Fig. 1. The improvement in resolution is clearly evident, particularly for shales that have a sizable aromatic component. This is because aromatic carbons have a larger chemical shift anisotropy than the aliphatic carbons. In the absence of spinning, the aromatic carbons yield broad anisotropic line shapes. Note also that for the spinning spectra, the maximum intensity of the aromatic band shifts to the isotropic value, which lies between the perpendicular and parallel components of the chemical shift tensor. 

Spectrum a was obtained without decoupling, and spectrum b was obtained with strong (43 kHz) H and F decoupling. The spectral contribution from the methyl carbons was subtracted from these spectra [10]. The residual resonance line shape observed is due to the chemical-shift anisotropy of the central carbon in a powdered sample. The effects of chemical-shift anisotropy will be discussed in later in this chapter. 

Effect of chemical-shift anisotropy on line shapes ... 

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