One-carbon unit transfer reaction of imidazolinium (a model of folate cofactor) with 1,2-diaminobenzene has been studied using PM3 semi-empirical molecular orbital calculations. The results show that there are two pathways to complete this reaction because the imidazolinium ring has two different breaking patterns. These two ways both 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.

Key words: PROTON TRANSFER, FOLIC ACID, COENZYME, MODEL COMPOUND, SEMIEMPIRICAL EQUATIONS, QUANTUM CHEMISTRY, BENZENEDIAMINE P, TRANSPOSABLE ELEMENT, C1 CHEMISTRY