NMR-STUDY OF THE CONFIGURATION AND PROTONATION EQUILIBRIA OF A PYRAZOLOTRIAZOLE AZOMETHINE DYE

H-1 NMR and NOE spectroscopy have been used to investigate the ground state configuration and proton equilibria of a 7H-pyrazolo[5,1-c][1,2, 4]triazole phenylamino azomethine dye. NOE experiments show that the d ye exists in the syn configuration at room temperature. Two protonatio n equilibria can be identified in CDCl3-CF3CO2H at 1.6 +/- 0.2 and 0.0 +/- 0.2 -log[acid] units. The first equilibrium involves protonation of the azomethine nitrogen and leads to changes in the NMR spectrum wh ich are interpreted as arising from increasing deviation from planarit y about the azomethine bond because of steric interactions. The second equilibrium involves protonation of the phenylamino nitrogen.