Manifestations of intramolecular H-bonds of CH ... O and OH ... C type in quercetin molecule: Analysis of IR spectra by mean of density functional theory ...

The IR spectra of 48 conformers of quercetin which represent full conformation space of its tautomers have been modeled at B3LYP/6-311++G(d,p) level of the density functional theory. The presence of intramolecular H -bonds C2 ' H/C6 ' H...O3 and O3H...C2 '/C6 ' was characterized by their spectral manifestations. The C2 ' H/C6 ' H... O3 contacts were found to have a spectral blue-shift. The O3H...C2 '/C6 ' contacts were mostly red-shifted. The stretching vibrations of H-bonds C2 ' H/C6 ' H...O3 demonstrate an increase in the intensity of the modes of stretching vibrations nu(C2 ' H)/nu(C6 ' H) and an increase in the frequency of their out-of-plane vibrations gamma(C2 ' H)/ gamma(C6 ' H). Most of the spectral parameters correlate a little with the energy of the H-bonds.