Tautomerism Of Heteroaromatic Compounds Research Articles

Tautomerism of heteroaromatic compounds with five-membered rings. 14. Confirmation of the structure of Reissert salts as condensed 5-aminooxazolium cations

Tautomerism of heteroaromatic compounds with five-membered rings. 14. Confirmation of the structure of Reissert salts as condensed 5-aminooxazolium cations

The tautomerism of heteroaromatic compounds with 5-membered rings—XI: 4-Hydroxyisoxazoles-4-isoxazolinones

Four 4-hydroxyisoxazoles together with model compounds have been investigated by UV, IR and NMR spectroscopy and by p K a measurements, 4-Hydroxyisoxazoles exist predominantly in the hydroxy-form in a wide range of media.

The tautomerism of heteroaromatic compounds with five-membered rings. Part XII. The imidazole 3-oxide versus 3-hydroxy[3H]imidazole equilibrium

Spectroscopic and pKa value comparisons with model compounds indicate that benzimidazole 3-oxide exists predominantly in the NH-form in aqueous solution, but predominantly in the OH-form in non-polar solvents. For 2,4,5-triphenylimidazole 3-oxide, steric hindrance in the N-methyl model complicates matters, but this compound appears to exist as comparable amounts of OH- and NH-forms in aqueous solution and in the OH-form in non-polar solvents. The structures of these compounds in the solid state are discussed.

The tautomerism of heteroaromatic compounds with five-membered rings. Part XIII. The tautomeric structure of 1-methyl-5-methyl-aminotetrazole

The title compound exists very predominantly in the amino-form in dioxan, ethanol, water, and dimethyl sulphoxide solutions. In water, KT is of the order of 109.

The tautomerism of heteroaromatic compounds with five-membered rings—X : 1-Phenyl-1,2,4-traialzolidine-3,5-dione

1-Phenylurazole is shown by physical measurements to exist predominantly in the dioxo form (I). The structures of its anion and mono-methyl derivatives are also discussed.

The tautomerism of heteroaromatic compounds with five-membered rings—VIII

The constitution is discussed of the various compounds described in conflicting literature claims as phenyl-hydroxy-oxadiazoles, and authentic specimens of several of the isomers are described. Spectroscopic measurements and pK values show that 3-hydroxy-1,2,4- and -1,2,5-oxadiazoles exist predominately in the hydroxy-form, whereas 2-hydroxy-1,3,4- and 5-hydroxy-1,2,4-oxidiazoles occur mainly as the corresponding oxadiazolinones. These results are related to the general pattern of tautomeric behaviour in the hydroxy-azole series.

The Tautomerism of heteroaromatic compounds with five-membered rings—IX

Abstract The complex tautomerism of N-unsubstituted pyrazolin-3(5)-ones has been elucidated by UV spectroscopy and basicity measurements. For aqueous solution (polar medium) the stability of the forms is II > IV ??? III, I whereas for cyclohexane solution (nonpolar medium) the order is IV > I ??? II, III.

The tautomerism of heteroaromatic compounds with five-membered rings—V: 1-Substituted 3-hydroxypyrazoles

Spectroscopic and basicity evidence shows that 3-hydroxy-1,5-dimethyl- and 3-hydroxy-5-methyl-1-phenyl-pyrazole exist in the hydroxy form in non-polar media and in the solid state. In aqueous solution the hydroxy- and oxo-forms co-exist in comparable amounts.

The tautomerism of heteroaromatic compounds with five-membered rings—IV : 1-substituted pyrazolin-5-ones

The IR, UV, and NMR spectra and p K values are discussed of six potentially tautomeric 1-phenyl and 1-methyl-pyrazolin-5-ones. These compounds exist under most conditions in non polar media in the Δ 3-form. In aqueous solution that NH-formis in equilibrium with ca.10% of the OH-form. The effect of substituents, and the relation of the results to those for the corresponding isoxazolin-5-ones is discussed. Previous work is reviewed.

The tautomerism of heteroaromatic compounds with five-membered rings—VII : Isoxazolin-3-ones—3-hydroxyisoxazoles

The preparation of some 3-hydroxyisoxazoles from β-keto-esters and the proof of their structure is described. These compounds are shown to exist largely in the hydroxy form.

The tautomerism of heteroaromatic compounds with five-membered rings—III

The tautomerism of heteroaromatic compounds with five-membered rings—III

The tautomerism of heteroaromatic compounds with five-membered rings—II : 3-,4- and 5-amino- and acetamido-isoxazoles

Infra-red and nuclear magnetic resonance spectra show that all types of amino- and acetamido-isoxazoles exist predominantly as such. Ultra-violet spectroscopy indicates that 3- and 5-amino-isoxazoles are protonated at the ring nitrogen atom, but the 4-amino- analogues on the amino- group. Basicities of these compounds are recorded.

The tautomerism of heteroaromatic compounds with five-membered rings—I : 5-hydroxyisoxazoles-isoxazol-5-ones

Infra-red and ultra-violet spectra show that 3,4-dimethyl-5-hydroxyisoxazole exists in aqueous and chloroform solution, and in the solid phase in the OH form; and that 3-phenyl-, 4-bromo-3-phenyl-, and 4-methyl-3-phenyl-isoxazol-5-ones exist as mixtures of the CH and NH forms in solution, the proportion of the NH form increasing with the polarity of the solvent. The basicities of isoxazole and some of its derivatives are recorded. Isoxazol-5-ones are acids of comparable strength with carboxylic acids.