The possible tautomerism of the potential rotary switch 2-(2-(2-Hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-dione

Isomerization and aggregation of 2-(2-(2-hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-dione: Recent evidences from theory and experiment

“…2. Two conclusions can be drawn from it: the studied compound exists as E′ isomer in the solid state, which confirms previously made conclusions for its dominance in proton acceptor solvents [3] or in solvents with mixed nature like methanol or water (see relative stability in water as a guideline, Table 1); as predicted by the theoretical calculations, 1E′ is stabilized by formation of linear aggregates (Fig. S3) and as can be seen from Fig.…”

“…Taking into account that all four isomers are almost identical from the viewpoint of UV-Vis spectroscopy, their identification in DMSO was made by careful analysis of the NMR spectra of 1 by using 3 as a reference compound [3]. It was shown on basis of 1 H and 13 C spectra that E′ and Z′ forms are presented in solution as major and minor component, respectively, which matches the theoretical predictions very well.…”

“…Most probably the experimental spectra of both species are also almost identical and strongly overlaps, which could not bring UV-Vis spectral evidences for the selfassociation. The evidences are indirect: in the experimentally measured UV-Vis spectra [3] the observed changes are related only to the process of deprotonation in proton acceptor solvents at low concentrations (10 −5 M and lower) as a result of the aggregates' destruction according to the general equilibrium scheme:…”

“…The authors have stated that 1 exists as a mixture between azo and hydrazone tautomers in methanol and dimethyl sulfoxide (DMSO). Recently we have investigated the spectral behaviour of 1 in a variety of solvents, proving that the conclusions previously made for the existence of the azo tautomer are wrong [3]. The combined use of UV-Vis spectroscopy, NMR ( 1 H and 13 C) and theoretical calculations has shown that the investigated compound exists as a mixture of isomers of the hydrazone tautomer, generally assigned as E-oriented (major form) and Z-oriented (minor form) in Scheme 1.…”

“…It was concluded that their stabilization depends on the solventstructures 1E′ and 1Z′ are presented in DMSO possibly as a result of a solute-solvent interaction. Compound 1 spontaneously deprotonates at low concentrations and aggregates at high concentrations (10 −4 M and higher) according to the UV-Vis investigations [3]. These two processes are linked and depend strongly on the solvent.…”