Abstract: Using the method of density functional theory B3LYP, we investigated the chiral transition process of the phenylalanine molecule in the situation of dualwater at the level of 6-311+G(2-df-). We drew a reaction potential energy surface for chiral transition path by finding the structures of extreme value points including the transition states and intermediates, and analyzed the geometric and electronic structure properties of extreme value points. The results sh
ow that the H atom on the chiral C atom of S-3-Phe&2H₂Ophenylalanine molecule can transfer to the other side of the C atom via the O atoms of carboxyl atoms as a bridge, and achieve the chiral transition of phenylalanine molecule from S-3-Phe&2H₂Otype to R-3-Phe&2H₂Otype. On this path there are four intermediates and five transition states. The maximum reaction energy barrier is 221854 8 kJ/mol, which comes from the fourth transit
ion state TS₂-R-3-Phe&2H₂O.

Key words: phenylalanine, transition state, chirality, density functional theory