Isotopic effect on tautomeric behavior of 5-(2,6-disubstituted-aryloxy)-tetrazoles

Isotopic splitting patterns in the (13) C NMR spectra of some partially deuterated 1-aryl-2-(phenyldiazenyl)butane-1,3-dione and 4-hydroxy-3-(phenyldiazenyl)-2H-chromen-2-one: evidence for elucidation of tautomeric forms

Nuclear magnetic resonance spectra of synthesized azo dyes derived from aniline derivatives in reaction with benzoylacetone and 4-hydroxycoumarin were studied in both CDCl3 and (CD3 )2 SO (two drops of D2 O were added into solutions of dyes). All dyes showed intramolecular hydrogen bonding. Dyes derived from o-nitro aniline in the reaction with benzoylacetone, and 4-hydroxycoumarin showed bifurcated intramolecular hydrogen bonds. The solvent-substrate proton exchange of dyes derived from benzoylacetone and 4-hydroxycoumarin was examined in the presence of two drops of D2 O. Among ten dye samples, two dyes derived from benzoylacetone did not show deuteration, three dyes showed partial deuteration and five dyes showed full deuteration under similar conditions. For the partially deuterated dyes the β-isotope effect in (13) C splitting was investigated and was used for the determination of the predominant tautomeric form.

Prototropic tautomerism of 5-aryloxy-1(2)H-tetrazoles

The structure of 5-(2,6-dimethylphenoxy)-1H- and 2H-tetrazoles together with those of 5-(2,6-diisopropyl-phenoxy)-1H and 2H-tetrazoles have been theoretically studied including absolute shieldings and energies. The conclusion of these studies is that a slow tautomerism between 1H- and 2H-tetrazoles cannot explain the experimental observations reported recently in the literature.