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Tautomerism in azo dyes: Border cases of azo and hydrazo tautomers as possible NMR reference compounds

Deneva, Vera ; Lyčka, Antonin ; Hristova, S. ; Crochet, Aurélien ; Fromm, Katharina M. ; Antonov, Liudmil

In: Dyes and Pigments, 2019, vol. 165, p. 157–163

In order to meet the need for NMR reference compounds in the study of tautomeric azo dyes, two series of azo dyes, derived from 3-methyl-1-phenyl-4- (phenyldiazenyl)-1H-pyrazol-5-amine and 5-methyl-2-phenyl-4-(2- phenylhydrazono)-2,4-dihydro-3H-pyrazol-3-one, have been studied by using molecular spectroscopy (UV–Vis and NMR) and quantum-chemical calculations (M06- 2X/TZVP) in solution. The...