KETO AND ENOL TAUTOMERS OF 4-BENZOYL-3-METHYL-1-PHENYL-5(2H)-PYRAZOLONE

The tautomeric keto and enol forms of 4-benzoyl-3-methyl-1 -phenyl-5(2 H)-pyrazolone, C17H14N2O2, have been prepared and their crystal struct ures characterized by X-ray analysis. The unit cell of the enol form, 4-benzoyl-5-hydroxy-3-methyl-1-phenylpyrazole, contains two structural conformers. The intramolecular distances in the enol form [2.621 (3) and 2.663 (2) Angstrom] indicate the presence of hydrogen bonds, while the corresponding distance in the keto form [3.079(3) Angstrom] does not. In the keto form there is an intermolecular hydrogen bond [2.673( 3) Angstrom] between the imino N(2) atom and the carbonyl O(1) atom.