Isotropic chemical shifts INDEX

Constant in Eq. (1) - for interpretation see text Sideband pattern index Isotropic chemical shift... 

In NMR experiments one can only measure the CSs in a limited set of points in space (the nuclei positions r ). However, the induced field and, consequently, the nuclear shielding tensor, are defined and can be computed for aU points in space such that one can drop the index i from Equation 12.4 and calculate the shielding tensor at any arbitrary position r, yielding the so-called nucleus-independent chemical shifts (NICS) [24]. NICS values are, thus, not referenced with respect to any nucleus and that is why they are nucleus independent. Also, and similarly to site-specific shieldings, rather than dealing with the shielding itself, one frequently reports the isotropic NICS shift (5j, j,5) defined as follows ... 

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