Abstract: The reaction mechanism of phenol with hydrogen peroxide radical attacking its para and ortho positions in water was proposed and investigated by Density Functional Theory(DFT) method at UB3LYP/6-311G ^** UB3LYP/6-31G^* computational level. It is found that there are three transition states and three intermediate complexes along each of the reaction path, and the transition states are confirmed through frequency analysis. According to the topological analysis of molecular charge density, it is found in reaction(1), that two hydrogen bonds were formed at the IM₁ and TS₁, two ring structures(a five-membered ring and a six membered ring) were formed simultaneously. The results of the energy(including single point energy correction and the solvent effect of water) calculation show that the main activation energies of the two reactions are approximately the same, which indicates that both of the two reactions may occur. This is in accordance with the practical experiment that the catechol and hydroquinone both exist in the product mixture.

Key words: Diphenols, DFT, Transition states, Hydrogen bond, Topological analysis of charge density