H-1, C-13 and N-15 NMR study of some triazolo- and tetrazolopyridazines and thioxotriazolopyridines

H-1, C-13 and N-15 NMR data are reported for nine azoloazines. From the res ults obtained it is found that the N-15 chemical shifts are particularly we ll placed to provide reliable data on both the structures of the compounds studied and on their potential to undergo valence and prototropic tautomeri sm. Of particular note is the high sensitivity of the N-15 chemical shifts to changes in the nitrogen electronic environment. In the present work up t o seven inequivalent nitrogen atoms may occur in a given molecule and they are readily distinguishable by means of their different N-15 chemical shift s. Some ab initio calculated molecular properties (C-13 and N-15 shieldings , partial charges and total SCF energies) were used in the confirmation of the NMR signal assignments, in the prediction of the protonation site and a lso in the estimation of the most stable tautomers of the compounds studied . Copyright (C) 1999 John Wiley & Sons, Ltd.