STRUCTURAL AND VIBRATIONAL STUDY OF 3-HYDROXYFLAVONE AND 3-METHOXYFLAVONE

Most stable molecular structures of 3-hydroxyflavone and 3-methoxyflavone have been investigated by semiempirical calculations (AM1 method) at the state of isolated molecule. For 30HF, the comparison between Xray diffraction data and calculated structural parameters shows a major modification in the inter-ring linkage with a rotation of the phenyl ring with regard to the rest of the molecule. This rotation of the B-ring is not observed in the 30MeF,but the orientation of the methoxy group changes with the physical state. The predictions about the conformational modifications with the physical state of these molecules have been confirmed by vibrational spectroscopy. For the 30HF molecule, the comparison between the solid and solution Raman spectra shows that the 1200-1400 cm(-1) spectral range is particularly affected, seeing that the inter-ring stretching vibration contributes to a great number of normal modes. 30MeF Raman spectra are less perturbed by the change of physical state, only two small frequencies shifts are observed. In order to assign the most important perturbation in the spectra of the two molecules, the vibrational frequencies have been computed to determine the atoms and groups involved in each normal mode.