ASSESSMENT OF SOLVENT-INDUCED NITROGEN SHIELDING VARIATIONS OF TRIAZOLE SYSTEMS

High-precision N-14 NMR shieldings are reported for all of the possibl e N-methyl triazoles in a variety of solvents. A large difference is o bserved in the effects of solvent on the shieldings of the pyrrole-typ e and pyridine-type nitrogen atoms in such systems. This difference la rgely arises from solvent-to-solute hydrogen-bonding effects for the l atter type of nitrogen atom. For these two types of nitrogen atoms in triazoles, solvent polarity effects induce changes in the shieldings i n opposite directions: this is corroborated by shielding calculations using the solvaton model. Solvent-to-solute hydrogen-bonding effects a re larger than those due to solvent polarity and permit the assessment of the basicities of nonequivalent nitrogenous sites; these appear to parallel the analogous basicities with respect to protonation. (C) 19 95 Academic Press,Inc.