Solvent polarity and hydrogen-bonding effects on the nitrogen NMR shieldings of N-nitrosamines and DFT calculations of the shieldings of C-, N-, and O-nitroso systems.

High-precision nitrogen NMR shieldings, bulk susceptibility corrected, are reported for dimethyl-N-nitrosamine (I) and diethyl-N-nitrosamine (II) in a variety of solvents which represent a wide range of solvent properties from the point of view of polarity as well as hydrogen bond donor and acceptor strength. The observed range of solvent-induced nitrogen shielding variations of (I) and (II) is significant for the amino-type nitrogens, up to about 16 ppm, and originates essentially from the deshielding effect of the increasing polarity of solvent. On the other side, the nitroso nitrogen shieldings reveal an even stronger response to solvent effects, within about 20 ppm, but in this case the increasing polarity and hydrogen bond donor strength of solvent produce enhanced shielding.

A study of solvent polarity and hydrogen bonding effects on the nitrogen NMR shielding of isomeric tetrazoles and ab initio calculation of the nitrogen shielding of azole systems.

High-precision nitrogen NMR shieldings, bulk susceptibility corrected, are reported for the N-methyl derivatives of the two existing isomeric tetrazoles (I, II) in a variety of solvents which represent a wide range of solvent properties from the point of view of polarity as well as hydrogen bond donor and acceptor strength. The observed range of solvent-induced nitrogen shielding variations of I and II is significant for the pyrrole-type nitrogens (N-Me), up to 9 ppm, and even more so for pyridine-type nitrogen atoms, where it can attain a value of 20 ppm. There is a clear distinction between the two types of nitrogen atoms in that the former exhibit a deshielding effect with increasing polarity of the medium while the latter experience an increase in the magnetic shielding of their nuclei.