Effect of different Substiuents on Uracil and its 2-Hydroxy-4-oxo Enol

Tautomer-A Theoretical Study

^{The uracil \2 - Hydroxy-4-oxo Uracil tautomeric system was stdied by employing the MNDO semi –empirical method for the calculations. The  uracil structure was found to be energetically favourable as indicated by the calculated heat of formation,theGibbs free energy,the HOMO and LUMO energies, and  charges. The substitution by F,OH,NH,CH,and BH at the carbon-6 position was found to affect the geometrical parameters of the substituted molecules. All of the substituents were found to shift the equilibrium in forward direction compared to the unsubstituted  tautomeric pair as indicated by the calculated values for the equilibrium  constants}