Theoretical Modeling of the Ground State Intramolecular Proton Transfer in Cytosine: DFT Level Study

Five isomers of cytosine and their mutual interconversions were studied theoretically at the B3LYP level using basis sets 6-31G and 6-311G and a different number of polarization and diffuse functions. It was demonstrated that the canonic aminooxo tautomer of cytosine is the most stable one. However it has a non-planar geometry. It was shown that the energies and energy barriers of the studied systems are sensitive to the inclusion of polarization functions in the basis set, but they have lesser sensitivity toward inclusion of diffuse functions.