Tautomeric behaviour and isotopic multiplets in the 13C NMR spectra of partially deuterated 5-arylazo-pyrimidine (1 H,3H,5H)-2,4,6-triones and 5-arylazo-2-thioxo-pyrimidine (1H,3H,5H)-4,6-diones - Evidence for elucidation of tautomeric forms

Abstract

NMR spectra of the synthesized azo dyes, 5-arylazo-pyrimidine (1H,3H,5H)-2,4,6-triones (5a-g), 1,3-dimethyl-5-arylazo- pyrimidine (1H,3H,5H)-2,4,6-triones (6a-g), and 5-arylazo-2-thioxo-pyrimidine (1H,3H,5H)-4,6-diones (7a-g) were studied in (CD3)2SO (three drops of CD3OD were added into solutions of the dyes in two different concentrations). All dyes showed intramolecular hydrogen bonding. Dyes 5a-7a showed bifurcated intramolecular hydrogen bonds. Tautomeric behaviours of some of W -methylated azo dyes (6a-g) were studied in two different concentrations. The solvent-substrate proton exchange of dyes 5a - d, 6a and 7a - e was examined in presence of three drops of CD3 OD. The dyes which were soluble in (CD3)2 SO containing CD2OD showed isotopic splitting (β-isotope effect) in the 13C NMR spectra. © 2009 John Wiley & Sons, Ltd.