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

The molecular and crystal structures of 4-acetamido-2,3-dimethyl-1-phenylpyrazol-5-one (1) and 4-maleylamido-2,3-dimethyl-1-phenylpyrazol-5-one (2) were studied. The molecular conformations are stabilized via systems of intermolecular hydrogen bonds between the amide groups and the carbonyl oxygen atoms of the pyrazolone rings. The conformation of compound 2 is additionally stabilized via an intramolecular interaction between the carboxyl group and the amide oxygen atom. According to the IR spectral data, protonation of the compounds understudy in an acetonitrile solution occurs at the carbonyl oxygen atom of the pyrazolone ring, which is also confirmed by the UV spectral data.