Tautomeric behaviour and isotopic multiplets in the 13C NMR spectra of partially deuterated 5‐arylazo‐pyrimidine (1H,3H,5H)‐2,4,6‐triones and 5‐arylazo‐2‐thioxo‐pyrimidine (1H,3H,5H)‐4,6‐diones—evidence for elucidation of tautomeric forms |
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Authors: | Nader Noroozi Pesyan |
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Institution: | Department of Chemistry, Faculty of Science, Urmia University, 57159 Urmia, Iran |
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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 N‐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 CD3OD. The dyes which were soluble in (CD3)2SO containing CD3OD showed isotopic splitting (β‐isotope effect) in the 13C NMR spectra. Copyright © 2009 John Wiley & Sons, Ltd. |
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Keywords: | NMR 13C NMR 1H NMR solvent– substrate proton exchange β ‐isotopic effect bifurcated intramolecular hydrogen bond tautomeric behaviour 5‐arylazo‐pyrimidine (1H 3H 5H)‐2 4 6‐triones 5‐arylazo‐2‐thioxo‐pyrimidine‐(1H 3H 5H)‐4 6‐diones 1 3‐dimethyl‐5‐arylazo‐pyrimidine (1H 3H 5H)‐2 4 6‐triones |
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