NMR study of the configuration and protonation equilibria of a pyrazolotriazole azomethine dye

Abstract

¹ H 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 dye exists in the syn configuration at room temperature. Two protonation 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 which are interpreted as arising from increasing deviation from planarity about the azomethine bond because of steric interactions. The second equilibrium involves protonation of the phenylamino nitrogen.