15N, 13C and 1H NMR study of tautomerism in 2-(phenyldiazenyl-4-substituted naphthalen-1-ols. Influence of substitution in passive components on azo-hydrazo tautomerism

The neglected tautomerism in “Study of the electronic effect and quantitative spectra predictions of o-methoxyanilineterminated monoazonaphthols: a combined experimental and DFT study” by Guoxun Zhu, Yan Lin, Wenxian Zhou, Huacan Song and Zhengquan Li, RSC Advances, 2023, 13, 33736

“…Although it is believed that electron donating substituents in the phenyl ring shift the tautomeric equilibrium in 1 towards A-tautomer, 4 exactly the opposite is seen comparing 3 and 3d. Very recently Neuerová and Lyčka 53 have shown that the effect is exactly opposite in the case of nitro substituted in the naphthyl ring derivatives of 3, which validate the current theoretical prediction. The same hydrazone stabilization can be stated for 3d,e,g, where the substitution in 3b is modeled.…”

Do Phenyl Substituents Affect the Properties of Azobenzocrown Derivatives?

“…The contribution of tautomers, estimated from 1 H NMR spectra (at ∼10 −2 M), for 19‐membered p ‐hydroxyazobenzocrowns, namely 19‐ p ‐OH , t ‐Bu‐19‐ p ‐OH and Ph‐19‐ p ‐OH is shown in Figure 2 and listed in Table S1. Tautomeric equilibrium in solution depends on several factors, [45–48] including obviously the structure of the molecule and the properties of its chemical environment such as solvent type, pH, the presence of ionic species (e. g. metal salts) or temperature. For 19‐membered p ‐hydroxyazobenzocrowns we have recently postulated [38,39] that in polar solvents such as acetonitrile and DMSO, differing in hydrogen‐bonding affinity, the contribution of tautomers seems to be also connected with the presence of substituents in benzene rings.…”

“…The contribution of tautomers, estimated from 1 H NMR spectra (at ~10 À 2 M), for 19-membered p-hydroxyazobenzocrowns, namely 19-p-OH, t-Bu-19-p-OH and Ph-19-p-OH is shown in Figure 2 and listed in Table S1. Tautomeric equilibrium in solution depends on several factors, [45][46][47][48] including obviously the structure of the molecule and the properties of its chemical…”

Ketohydrazone dyes derived from 4-morpholino-2-naphthol and ortho-substituted anilines: Further examination of the hyperchromism induced by the 4-morpholino-2-naphthol moiety

“… 124 -130 as established by extensive 2D-NMR experiments (see supporting information for selected examples) and in accord with recent findings by Lyčka et al, for the C=N C-atom of 4-substituted 2phenyldiazenylnaphthalen-1-ols. [37] Unlike the established trend of decreasing chemical shift of C-2 with increasing donor strength of the para-substituent in the phenyl ring of ketohydrazone dyes [C-2 = 181.7 (p-NO2C6H4-), 170.8 (C6H4-), 161.0 (p-EtOC6H4-), 153.6 (p-Me2NC6H4-)] [24] in this work there is very little influence of the phenyl ring ortho-substituent upon the chemical shift of C-2 which resonates in a narrow range typical of that for ketohydrazone tautomers. [10,[23][24][25][26]30] Further NMR evidence to support the extensive preference of the ketohydrazone form in CDCl3 was garnered from the 19 F NMR spectrum of dye 3h, which exhibited a single signal at  -130.9 which was in good agreement with the data reported by Lyčka for the F atom of the dye derived from the coupling of 2-naphthol with 4fluroaniline wherein the  19 Fazo = -113 and  19 Fhydrazone = -130.…”