Chemical-shift anisotropy typical values

In a series of V wideline NMR studies, Mastikhin and coworkers have explored the chemical nature of the catalytically active species 37 2]. While the spectra of industrial catalysts from various sources are found to be substantially different, these differences more or less disappear after exposure to the reaction mixture. This result confirms the previously held view that the catalytically active species forms under operating conditions. Figure 4 shows typical spectra recorded at a field strength of 7.0 T, at which the lineshape is dominated by the chemical shift anisotropy. The principal contribution to the spectrum in Fig. 4 arises from an axially symmetric powder pattern with approximate 81 and 8 values of — 300 and — 1300 ppm, respectively. Based on comparative studies of model preparations, Mastikhin et al. suggest that the key compound formed has the composition K3VO2SO4S2O7. The anisotropic chemical shift parameters of... 

Rigid molecules should exhibit a broad signal with the typical shape of a line dominated by the chemical shift anisotropy. The principal values of... 

In the gas phase, above the minimum, the F spin-lattice relaxation time is linear with density p of the gas, and the slope (TJp) is found to be consistent with Ti/p)ccT in cases where temperature-dependent measurements of F relaxation have been carried out. This implies that the relaxation is dominated by the spin-rotation mechanism in the gas phase. In the liquid phase, the results for several molecules indicate that spin-rotation mechanism is dominant, especially at higher temperatures and intermolecular dipole-dipole mechanism contributes to the relaxation at lower temperatures, e.g., below 200 K in FCIO3. Intramolecular dipole-dipole mechanism, chemical shift anisotropy and scalar coupling contributions are usually found to be negligible in F relaxation. Where intermolecular dipole-dipole and spin-rotation mechanisms have been used to interpret results using Arrhenius temperature dependence for both, the activation energies are usually not equal. Some typical values of F spin-lattice relaxation times are shown in Table 4. 

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