Abstract: Based on density functional theory at the level of B3LYP/6-311+G(2df), we investigated the chiral transition process of the phenylalanine molecule under the cooperative action of monoH₂O. Further more, we drew a complete chiral transition path reaction potential energy surface of phenylalanine molecule  by searching for the extreme value point structures including 5 transition states and 4 intermediate, and analyzed the geometric and electronic structure properties of extreme value points. The results show that the H atom on the chiral C atom of Sphenylalanine molecule can transfer to the other side of the chiral C atom via the O atoms of carboxyl as a bridge under the cooperative action of monoH2O, to achieve the chiral transition of phenylalanine molecule from Stype to Rtype. On this path there is 4 intermediate and 5 transition states. The maximum reaction [JP+1]energy barrier is 200.588 2 kJ/mol, which comes from the fourth transition state TS₂-R-Phe&1H₂O-2.

Key words: phenylalanine, chiral, transition state