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 one-and two-dimensional N-15, C-13 and H-1 NMR spectra of benzenediazonium chloride coupling product with 4-R-naphthalene-1-ols (R = NO2 (1), Br (2), Cl (3), H (4), OCH3 (5)) were measured and analysed. It was found that the reaction products exist predominantly in hydrazone forms. Contrary to previously published influence of substituents in diazonium salts, where more electron acceptor types of substituents cause increase contents of hydrazo forms, the situation in compounds 1-5 is completely opposite. Moreover, hydrazone content in 4-nitro-2-[(E)-(4-nitro-phenyl)diazenyl]naphtalen-1-ol (6) combining substitution both in position 4 of passive component and position 4 of active component (i. e. diazonium salt) is higher compared with that in 4-nitro-2-[(E)-(phenyl)diazenyl]naphtalen-1-ol (1).

Automated summary

The one- and two-dimensional NMR spectra of benzenediazonium chloride coupling product with 4-R-naphthalene-1-ols were measured and analysed, revealing that the reaction products exist predominantly in hydrazone forms. Contrary to previous studies, it was found that more electron acceptor types of substituents actually cause an increase in hydrazone content in the compounds.