Computational Studies on the Ground State Tautomer,Hydrogen Conformations and Vibrational Spectroscopic Analysis of Antitumor Agents:3-Deazauracil and 6-Azauracil

The ground state hydrogen conformations and vibrational analysis of 3-deazauracil(3DAU)and 6-azauracil(6AU)tautomers(4-enol and 2,4-diol forms)have been calculated using ab initio Hartree-Fock(HF)and density functional theory(B3LYP)methods with 6-311++G(d,p)basis set level.The calculations have shown that the most probably preferential tautomer of 3DAU and 6AU are the 4-enol form,which gives best fit to the corresponding experimental data.The ground state conformer of the 2,4-diol form has two O—H bonds which are oriented externally and internally(to the N—H bond).The vibrational analyses of the ground state conformer of each tautomeric form of 3DAU and 6AU were done and their optimized geometry parameters(bond lengths and bond angles)were given.Furthermore,from the correlations values it was concluded that the B3LYP method is superior to the HF method for both the vibrational frequencies and the geometric parameters.