Abstract
The molecular and crystal structure of 5-amino-2, 4-dihydro-2-phenyl-3H-pyrazol-3-one was examined by the X-ray diffraction method to establish the predominant tautomeric form (the CH-form) due to the pyrazol-3-one ring. In the crystal, the molecules are linked by the intermolecular hydrogen bond between the NH2 and C=O groups to form four hydrogen bonds with three adjacent molecules. The title compound, C9H9N3O crystallizes in space group P21/a with lattice parameters a=10.187 (5), b=11.481 (4), c=7.392 (4) Å, β=102.43 (5)°, and Z=4.
