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

摘要

Theoretically predicted vibrational wavenum-bers 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.