The tautomeric structures of 3(5),3 '(5 ')-azopyrazole [(E)-1,2-di(1H-pyrazol-3(5)-yl)diazene)]: The combined use of NMR and electronic spectroscopies with DFT calculations

An azo derivative of 1H-pyrazole has been chosen to study the information obtained from different techniques for determining the structure of a non-crystalline compound in the solid-state and in solution. Syn-anti isomerism of the azo group, prototropic tautomerism of the 1H-pyrazole and rotation about the pyrazole-azo group resulted in 20 structures that were analyzed. Energy calculations, C-13 and N-15 chemical shifts, H-1-H-1 coupling constants and electronic spectra reduced the 20 possible structures to only one, the 3,3'-Z,Z-anti-azopyrazole. (C) 2012 Elsevier B.V. All rights reserved.