Ab initio theoretical studies of relative stabilities and IR spectrum of 5-methylcytosine tautomers

The structure and relative energies of the tautomers of 5-methylcytosine in the gasphase and in different solvents are predicted using MP2 and density functional theory methods. The order of stability for these tautomers is C3>C1>C2>C4>C5>C6 calculated by MP2 and C1>C3>C2>C4>C5>C6 calculated by the B3LYP method. Relative energy calculations are performed in wide range of solvent dielectrics and in all solvents the oxo-amino C1 is predicted as the most stable tautomer. The infrared spectra of two dominant tautomers are calculated in the gas phase using HF and density functional theory. Good agreement between calculated (DFT) and experimental harmonic vibrational frequencies is found.