Tautomeric Forms of 3-Formyl- 4-Hydroxycoumarin Arylhydrazones
Tautomeric forms of 3-formyl-4-hydroxycoumarin arylhydrazones were studied by 1H and 13C NMR spectroscopy, as well as X-ray structural analysis. These compounds were shown to exist primarily in the 4-hydroxycoumarin form both in DMSO solution, as well as in gas phase; the chroman-2,4-dione form was a minor component. According to X-ray structural analysis data, solid 3-formyl-4-hydroxycoumarin phenylhydrazone exists in the 4-hydroxycoumarin form.