The parameters shown in the figure are those recommended by IUPAC. There are other conventions used in the older literature and at times it can be confusing. The other conventions are described here by Klaus Eichele. The site also contains a very useful tool to convert the parameters from one convention to another. Thank you Klaus!
Wednesday, August 20, 2008
Measuring Chemical Shift Parameters for Spin I=1/2 Nuclei in the Solid State
The observed frequency of a spin I = 1/2 nucleus in a molecule depends on the orientation of the molecule with respect to the magnetic field. For powdered solid samples, all possible orientations of the molecules are present in the magnetic field and one obtains an envelope of peaks called a powder pattern. If one can neglect all other interactions (such as dipolar coupling), the powder line shapes are dominated by the chemical shielding interaction. These line shapes provide valuable electronic, geometrical and dynamic information about the molecule. The chemical shift parameters can be read directly or calculated trivially from the spectrum. These parameters are indicated in the figure below.