Accurate calculations of the oxo–hydroxy tautomers of uracil

The geometric structures of the three lowest-energy tautomers of uracil have been calculated at the 6-31G** SCF level. Their relative energies have been calculated with the inclusion of correlation and zero-point energy effects. The dioxo-form is predicted to be the most stable, with the 2-hydroxy-4-oxo and 2-oxo-4-hydroxy forms being higher in energy by 46 and 52 kJ mol–1, respectively.