15 N NMR study of ( E )- and ( Z )-2-(2-(2-hydroxy-4-nitrophenyl)hydrazono)-1-phenylbutane-1,3-diones. A suitable method for analysis of hydrazone isomers

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

“…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. Very recently Lycka [4], using 15 N NMR, reached the same conclusion for 1 and 2 in DMSO and deuterochloroform.…”

“…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. The recent study of Lycka has brought additional, 15 N NMR based, evidences for stronger stabilization of the E-oriented COMe group [4]. His conclusions are based on using 2 J( 15 N β , 13 C) constants of 1 in DMSO-d 6 .…”

“…The calculated results show for C-2′ in respect of N α values of 1.0 Hz corresponding to E′/Z′, while values for 2.9 Hz of C-6′ are calculated for the E/Z isomers. In the paper of Lycka the value 2 J ( 15 N α , 13 C-2′) was measured as 1.6 for the major isomer and 1.5 for the minor one, and no value for 2 J( 15 N α , 13 C-6′) is shown [4]. Consequently the combined use of 2 J( 15 N α , 13 C) and 2 J( 15 N β , 13 C) confirms the availability of 1E′ as a major component and 1Z′, as a minor ones, in solution.…”

“…S1. c Taken from [4], relative error ± 0.3 Hz for 2 J constants. The calculated structure as shown in Fig.…”

“…Therefore, in the current communication, we will theoretically check the reliability of the approach proposed by Lycka [4] and will use his data to suggest a general logical scheme for distinguishing between all four isomers. A combination between theoretical and experimental data will be used to prove the effects of the concentration and solvent in the stabilization of the E′ and Z′ isomers in dimethyl sulfoxide.…”