Abstract: Based on the frontier orbital theory, the effects of position and number of phenolic-OH on the antioxidation of plant flavonoids were systematically investigated by means of structural chemistry and semi-empirical calculation method of quantum chemistry. And the quantum parameters of characteristic structure reflecting the antioxidation of flavonoids were also obtained. And the relationship between fr and antioxidation of flavonoids was also investigated. The results showed that the phenolic-OH in C ring had higher fr than those in A ring, and the ortho phenolic-OH and meta- phenolic-OH had higher fr than para- phenolic- OH and suggested that the position of phenolic-OH in flavonoids had great effect on the antioxidation activity. With the increasing of phenolic-OH in C ring, the fr in both C ring and A ring would all increase, which indicated the increase of antioxidation of phenolic-OH in both C ring and A ring. And there also existed good line regression between Σfr and Tr. The structural characteristic parameter of Σfr calculated by semi-empirical calculation method of quantum chemistry could be used to predict the antioxidation activity of flavonoids.

Key words: flavonoids, antioxidation, quantum chemistry, AM1