Theoretical Study On Nuclear Magnetic Resonance Spectra Of TMS,Three-ring Compounds And Isoflavone Derivatives

TMS has been optimized by different levels and methods, such as HF, B3LYP in this paper. On the basis the absolute shielding values of TMS have been calculated by different basis sets and the four methods, such as GIACK IGAIM, CSGT, Single Gauge Origin provided by GAUSSION98 program. The results show that as far as theoretical level is concerned, B3LYP is superior to HF . As calculating nuclear magnetic spectra, the better result can been gotten by GIAO at same theoretical level. In the meantime, a "saturation" basis set is founded in the calculation.Quantum chemical calculation has been carried out to calculate structural optimization, IR spectra, NMR spectra of three-ring compounds which have been synthesized by our research group. The result indicates that using B3LYP and bigger basis sets in the structural optimization and NMR calculation can achieve better results . At the same time, the calculated NMR spectra by GIAO method are better than that by IGAIM. However, adding diffusion function has little effect on the structural optimization and NMR calculation. The calculated results for the synthesized compounds are well consistent with the experimental data. We have theoretically studied several intermediate products in the process of synthesis. The structures of the intermediate products have been proved. Ab initio investigations have been applied to isoflavone derivatives with p- substituents on B ring ,which are 1A~1H and 2A~2H compounds. Intramolecular hydrogen bonding has been formed in 1A~1H compounds whose bonding distance is 0.1668nm. Thus is oflavone derivatives form a four-ring cross conjugated system. NMR spectra characteristics of the compounds with 9- hydroxyl substituting hydrogen have been discussed. Because hydroxyl possesses the strong property of attracting electrons, the chemical shifts of adjacent carbon and adjacent hydrogen decrease owing to increase of electron cloud density and strengthening of shielding effect. However, the chemical shift of conjoint carbon has more increase. In addition, the effects of substituents onthe chemical shift have been discussed. The increase of electron cloud density in benzene induced by substituent groups has the following order: NH2>OH>OCH3>H>F>Cl>Br>NO2. The chemical shifts of ortho- and para-hydrogens increase along with substituent groups' supplying electron to benzene(except for IE and 2E). Substituent group have little effect on hydrogens of A and C ring. The chemical shift of para- carbon increases as substituent groups' supplying electron to benzene(except for IE and 2E) increases . The chemical shift of ortho- carbon hasn't distinct change rule. The results of theoretical calculation are fundamentally consistent with the experimental values.