Multiple Quantum NMR Experiments of Non-Integer

7 Multiple quantum NMR experiments of non-integer spin quadrupolar nuclei 

The isotropic shift and the quadrupole induced shift (QIS = Co(p)/Co(l), with Cs defined in Table 2.4) can readily be obtained from the data. Firstly, the 2D spectrum must be referenced correctly. To obtain the correct ppm scale in the FI dimension one must set the spectrometer frequency in the FI dimension to pVo. The shift reference is most readily set at the carrier frequency, i.e. the shift in ppm at the carrier frequency in the multiple quantum dimension Ft is the same as the shift in ppm at the carrier frequency in the single quantum dimension F2. This is valid for data obtained with or without delayed acquisition and processed with or without shearing. The isotropic chemical shift is the same for both the single quantum and the multiple quantum dimensions. The QIS is different in both dimensions, however, and is given by 

The position of the centre of gravity with p = 1 for the single quantum dimension and p = Am for the multiple quantum dimension, is given by 

Hence the isotropic shift can readily be retrieved using 

The isotropic second-order quadrupolar shift SFqs(I,p) can be derived directly from SFcs using a factor of —(10/17) (Equation 14 in Pike et al. 2000). The chemical shift scale factors are given in Table 3.5. 

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Multiple Quantum NMR Experiments of Non-Integer 161 Spin Quadrupolar Nuclei... 

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