Abstract
Oxazol-5(4H)-ones containing a furan and/or benzene ring in conjugation with the azlactone system have been investigated by IR and NMR spectroscopy. The IR absorption bands in the region of the C=O stretching vibrations measured in CHCl3 revealed a clear splitting due to Fermi resonance interaction. Compounds with a furan-2-yl substituent exert multilevel resonance when the first overtone of an in-plane scissoring deformation γ of the furan ring interacts with the fundamental carbonyl stretching mode. A correlation has been found between the wavenumbers of the C=N stretching vibration and the 13C NMR chemical shifts of the carbon in the C=N bond. Spectral characterisation (UV-VIS, 1H and 13C NMR), configurations and optimum conformations of these compounds are given.