A Theoretical Study of the Interaction Between Cytosine and BX3 (X = F, Cl) Systems

The B3LYP method of DFT and HF theories of ab initio with 6-311+G** basis sets were used to predict the geometries of the cytosine-BX3 (X,=F, Cl) complex systems. Four conformers were obtained with no imaginary frequencies, respectively. The binding energies, enthalpies and Gibbs energies of cytosine-BX3 have been obtained. The analyses of the combinations between cytosine and BX3 using the natural bond orbital (NBO) method and thermodynamics indicate that the complexes (a) and (e), which depend on the proton affinities of the oxygen on the cytosine and boron in BX3, are the most stable ones with their combination energies of −234.21 and −228.23 kJ.mol−1 (B3LYP method, BSSE corrected). Based on the calculation results, a reasonable method was employed to calculate the change in the enthalpies and Gibbs energies to form eight complexes in the gaseous state at 298.15K and 101.325 kPa. It can be shown that the conformers (a) and (e) are the most stable and form readily.