Fig. 16.6. Schematic illustration of the anisotropy of the chemical shift tensor , leading to a qualitative understanding of the NMR lineshape change as a function of temperature in C70. (a) When the molecule is static, one expects a fully broadened spectrum from the chemical shift anisotropy. (b) When the C70 molecule rotates about cr22 uniaxi-ally, then crn and cr33 are expected to be averaged by rotation, while <j22 is almost unaffected by the uniaxial rotation, (c) When the molecule rotates isotropically, all the principal values of the chemical shift tensor should be averaged out to (o-,, + <r22 + a-33)/3 [16.18],

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