Abstract: Folic acid cofactor plays an important part in different enzymatic one-carbon unit transfer reactions. Its functions have been imitated a lot experimentally by using simple chemical models. One-carbon unit transfer reaction of imidazolinium with 1,2-diaminobenzene has been studied with PM3 semi empirical molecular orbital calculations in this paper. The results show that there are two ways to complete this reaction because the imidazolinium ring has two different breaking patterns. Both of these two ways have six steps, including two proton migrating steps that limit the reaction rate. The structures and energies of the intermediates and transition states have been calculated. All the intermediates and transition states have different conformations, and the reaction of classical conformations has been studied carefully.

Key words: 5,10-CH⁺-THF, One-carbon unit transfer, 1,2-Diaminobenzene, PM3 method, Theoretical study