Nitrogen nuclear shielding solvent effects

To try to reproduce the solvent effects on nitrogen nuclear shieldings of diazines and understand the physics beyond them we have applied the QM/continuum (PCM) and QM/MM(pol) (DPM) approaches described in the previous sections. 

We have presented and compared different solvation models (continuum, discrete, continuum + discrete) to study solvent effects on molecular properties. In particular, the nitrogen nuclear shielding, which is known to be very sensitive to even small modifications of electronic and/or nuclear charge distributions, has been analyzed. Such alternation/combination of different models has been required to study the complex nature of solute-solvent interactions when both long-range polar and shorter-range specific H-bond effects are active. 

Solvent effects can be produced by specific interactions, such as protonation or hydrogen bonding and nonspecific interactions which may arise from solvent polarity effects. Both of these types of interaction are found in studies of solvent effects on nitrogen nuclear shieldings. The extent of substituent effects depends upon the position of substitution and the electronic nature of the substituent. 

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. 

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