The bare reaction of chiral transition of ibuprofen molecules and the mechanism of waterassisted proton transfer from carbon to carbonyl were studied using the B3LYP method of density functional theory and the MP2 method of perturbation theory. The molecular structure analysis showed that the hydrogen bond angles corresponding to the eight membered ring transition state bTS2·2H

2

O

and the ten membered ring transition state bTS2·3H

2

O in the processes of water-assisted proton transfer from carbon to carbonyl were all much larger than that corresponding to the six membered ring transition state bTS2·1H

2

O. Moreover the eight membered ring structure of transition state bTS2·2H

2

O was almost coplanar

and the ten membered ring structure of transition state a_TS1·3H

2

O/bTS2·3H

2

O was obviously out of plane. The study on the reaction path showed that there were six paths in the title reaction

where respectively proton only using ketonic O or methyl C and carbonyl O or carbonyl and benzene ring as the transfer bridge from one side to the other of chiral C. Calculations of potential energy surface showed that the path using proton was the dominant reaction channel

and carbonyl and benzene ring as the transfer bridge was the dominant reaction path. The Gibbs free energy barrier of the rate-determining step of bare reaction was 287.1 kJ·mol

-1



which would be reduced to 144.9 kJ·mol

-1

because of the chains constituted by two water molecules. The results showed that the chiral transition of ibuprofen molecules could be realized in multiple paths and the water molecules had a better catalysis on H transfer heterogeneous reaction of ibuprofen molecules

as well as the presence of water molecules in the body of a life

temperature fluctuations

molecular frequent collisions and the action of some enzyme conditions were the cause of S-Ibu optical isomers.