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

Abstract

The IR, UV, and NMR spectra and pK 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 Δ3-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. © 1964.