From DFT calculations, it has been carried out as B3LYP/6-31G** for the optimized structures and the predominant tautomer of benzalbarbituric acid (Benzal-BA) has been defined taking in consideration the total energy of the density functional theory. The structures of the possible tautomers of Benzal-BA have the C1 symmetry point group. Also the normal coordinate analyses via B3LYP/6-31G** have been calculated for the tri-ketonic Benzal-BA and compared with the scanned infrared spectrum. The hydrogen bonding, the orientation energy of the polar solvent and the free energy of formation of the solute-polar solvent complex (Benzal-BA/MeOH) were determined from the studies of the mixed solvents spectra. Structural DFT studies of some complexes have been carried out for the Benzal-BA with divalent Cu++ and with the optimized structure of Zn++ complex. From the optimized structures, it has been concluded that the structure of Cu(Benzal-BA)2 complex has C2h point group symmetry but Zn(Benzal-BA)2 complex has C1 point group symmetry. The structure of the Benzal-BA metal ion complex has been verified by comparative infrared spectra studies.