X-ray diffraction analysis and spectral studies of new derivatives of pyrazol-5-one

The molecular and crystal structures of 4-acetamido-2,3-dirnethyl-1-phenylp yrazol-5-one (1) and 4-maleylamido-2,3-dimethyl-1-phenylpyrazol-5-one (2) w ere studied. The molecular conformations are stabilized via systems of inte rmolecular hydrogen bonds between the amide groups and the carbonyl oxygen atoms of the pyrazolone rings. The conformation of compound 2 is additional ly stabilized via an intramolecular interaction between the carboxyl group and the amide oxygen atom. According to the IR spectral data, protonation o f the compounds under study in an acetonitrile solution occurs at the carbo nyl oxygen atom of the pyrazolone ring, which is also confirmed by the UV s pectral data.