Spectroscopic studies of the keto and enol tautomers of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone

Molecular structures of the two tautomers of a beta-diketone 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) were studied by MS, UV, TR, and X-ray diffraction methods. The mass spectra show little difference for the two forms of PMBP, while there are notable differences in the IR spectra as KBr pellets and in the UV spectra in different solvents for the keto- and enol-PMBP. The keto-and enol-PMBP were stabilized respectively by intermolecular and intramolecular hydrogen bonds. The two types of hydrogen bonds were characterized by X-ray diffraction. Infrared spectrometric analyses depending on temperature were also performed to study the thermal properties of PMBP. (C) 1996 Academic Press, Inc.