A joint application of vibrational spectroscopic and quantum mechanical methods in quantitative analysis of baicalein structure

Abstract

Theoretically predicted vibrational wavenumbers of baicalein were compared with available infrared (IR) and Raman experimental data. Assignments of the experimentally obtained normal vibrational modes were done using density functional theory calculations with M05-2X functional and the 6-311+G(2df,p) basis set implemented in the Gaussian 09 package. According to the results, the 1,700 to 1,400 cm -1 Raman and IR regions are associated with the double-bond character of the carbonyl group, aromatic in-plane skeletal vibrations, and aromatic character of the pyrone ring. In particular, the bands in the 1,650 to 1,550 cm -1 region represent the C=O and C2=C3 characteristic stretching modes. Most of the bands in the 1,500 to 650 cm -1 range involve C-C stretch, O-C stretch, and in-plane C-C-H, C-O-H, C-C-O, C-O-C, and C-C-C bending vibrations of the rings. Bands below 650 cm -1 are mostly assigned to different torsional modes of the rings. The applied method reproduced the experimental results with a high degree of accuracy. © Springer-Verlag 2012.