Introduction: Several molecular modelling techniques and quantum chemical methods
have been performed to correlate the chemical structures of the compounds with their physical
Methods: Theoretical parameters were used to characterize the molecular structure of the
investigated ligands and to study their equilibria mechanism. Molecular modelling data such as the
bond length, bond order, bond angles and dihedral angles values were estimated for some
pyrimidine compounds, where the data suggested the presence of tautomerism and dynamic
equilibria were deduced between all the detected tautomers in the solid state.
Results: Four main tautomers were predicted for barbital and thiobarbituric acid, while three
tautomers were for thiouracil. Quantum chemical parameters such as the highest occupied
molecular orbital energy (EHOMO), the lowest unoccupied molecular orbital energy (ELUMO), energy
gap (ΔE), dipole moment (μ), sum of the total negative charge (STNC), electronegativity (χ),
chemical potential (Pi), global hardness (η) and softness (σ) were calculated.
Conclusion: These studies display a good correlation between the theoretical and experimental data.