15N and 14N NMR spectra show that there is no valence tautomerism involving the nitro group in nitro derivatives of benzofuroxan systems and that the N-oxide function has a fixed position in the furoxan ring. Carbon chemical shifts of molecules with one, two or three furoxan rings attached to a benzene ring reveal additivity of effects which makes possible a complete and unambiguous assignment of the shifts.
Solvent effects on nitrogen shieldings are shown to vary from almost zero to about 26 ppm. These shielding variations can be analysed in terms of a variety of hydrogen bonding interactions and non-specific solute-solvent interactions. Steric effects are also taken into account. The non-specific interactions are found to be well accounted for by INDO/S-SOS shielding calculations incorporating the solvaton model. Nitrogen NMR is shown to be very suitable for distinguishing between a variety of solute-solvent interactions.
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