Functionalization of the C20 fullerene by pyridine and pyrimidine: A theoretical study

A theoretical study at the levels of CAM-B3LYP and MP2 was reported, with the aim of understanding the possibility of functionalization of the C-20 fullerene with pyridine and pyrimidine via a cycloaddition reaction. For this purpose, several [2+2] and [4+2] cycloaddition reactions were considered between C-20 and pyridine or pyrimidine, and their thermodynamic and kinetic parameters were calculated. The results indicated that those [4+2] cycloaddition reactions are favorable ones in which the fullerene plays the role of a dienophile. It was also found that a [4+2] reaction path in which it takes place via the formation of two new C-C bonds between two fragments, C-20 and heterocycle, is more favorable than that occurring via the formation of two different bonds, C-C and C-N. The calculation of global electron density transfer (GEDT) and molecular electrostatic potential (MESP) map revealed that the transition states are relatively polar and the C-20 fullerene acts as an electron acceptor. Determination of Frontier Effective-for-Reaction Molecular Orbitals (FERMOs) relevant to pyridine and pyrimidine satisfactorily described the reactivity of different active sites of pyridine and pyrimidine. Finally, the calculation of the reactions synchronicity showed that the reactions are relatively synchronous.