Paramagnetic nuclear shielding

Paramagnetic nuclear shielding as determined from the spin-rotation constant, see introduction. References... 

In many cases, experimental data have been discussed in terms of variations of the paramagnetic contribution, nuclear shielding constant (Equation (2)). Empirical correlations with parameters related to the electronic properties of other substituents in the molecule (electronegativities, Hammett substituent constants etc.) have been found. This kind of investigation has provided useful information about the electronic structure of the sulphur atom in different bonding situations and most of all about the electronic properties of the S-O bond, which is still a rather controversial matter. 

In Table 1-1 we thus report the N nuclear shielding (with its paramagnetic and diamagnetic contributions) and nitrogen lone pair natural population (NP(lp)) for the diazine showing the largest solvent effect, i.e., pyridazine, and its clusters in vacuo (VAC) and in the presence of an external PCM continuum. 

A relation between the paramagnetic susceptibility and the electromagnetic nuclear shieldings is easily established via Eqs. (196) and (203) ... 

NMR signal (compare the 6" Sn values of 5 and 8). Thus, paramagnetic effects as the result of Bo induced charge circulation involving the formally unoccupied Sn-pz orbital arises mainly from Sn-C or Sn-N bonds and to a minor extent from the lone pair of electrons at the tin atom. This explains that the dimerization of stannylenes causes a marked increase in Sn nuclear shielding since the Sn-p orbital is now used in donor-acceptor interaction. ... 

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