Spectral Properties of Novel 1,3-oxazol-5(4H)-ones With Substituted Benzylidene and Phenyl Rings

In the present work, five novel (4Z)-4-benzylidene-2-phenyl-1,3-oxazol-5(4H)-ones (azlactones) were investigated by the infra-red (IR) and nuclear magnetic resonance spectroscopy (NMR) of the 1H and 13C nuclei. The spectral properties of the oxazolone ring were monitored with respect to the substituents at the benzylidene and phenyl rings. The compounds were prepared by the Erlenmeyer–Plöchl synthesis from the respective substituted aldehydes and hippuric acid. The IR absorption spectra, measured in chlorophorm, showed a clear splitting of the vibration band in the region characteristic for the carbonyl stretching vibration. This splitting was attributed to the Fermi resonance and the unperturbed wavenumbers of the carbonyl stretching bands were calculated. The chemical shifts of the carbons of the oxazolone ring were assigned. The influence of substituents on spectral properties was demonstrated and discussed. It was found that the oxazolone molecule constitutes an extended π-electron system, with an efficient transmission of electron effects.