Abstract: Using the method of density functional theory B3LYP,  we investigated the third reaction channel of the chiral transition process of the nonrest
ricted area monomer methionine molecule at the level of B3LYP/6-311+G(2-df-). We drawed a complete reaction potentialenergy surface for chiral transition path of methionine molecule by finding the structures of the extreme value points in the reaction process, and analyzed the geometric and electronic structure properties of extreme value points too. The results show that the hydrogen atom on the chiral carbon atom of Smethionine molecule can transfer to the other side of the carbon atom via the 6C--10O atoms as a bridge, and achieve the third reaction channel of the chiral transition of methionine molecule from Stype to Rtype. On this path there are four intermediates and five transition states. The maximum reaction energy barrier is 321.361 2 kJ/mol, which comes from the second transition state TS₂-S3-Met.

Key words: non-restricted area, chirality, methionine, transition state