Tautomeric behaviors of 5-arylazobarbituric acids in different concentrations

Authors

Department of Chemistry, Faculty of Science, Urmia University, 57159, Urmia, Iran

Abstract

The NMR spectra of azo dyes, 5-arylazobarbituric (5a-g), 5-arylazo-1,3-dimethylbarbituric
(6a-g) and 5-arylazothiobarbituric acids (7a-g) were studied in DMSO-d6 in different
concentrations. An intramolecular hydrogen bond was observed and indicating that the
hydrazone forms is mostly predominant. The peak of the hydrazone proton was severely
broadened and its chemical shift appeared at down field due to intramolecular hydrogen bond.
Existence of nitro group at ortho-position on phenyl ring caused the chemical shift value of the
proton of hydrazone form in 5a-7a to be more deshielded than other hydrazone protons in 5bg−
7b-g due to bifurcated intramolecular hydrogen bond and anisotropic ring-current effect. Dyes
6 shows two tautomers in NMR time scale at low concentration in DMSO-d6.

Keywords


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