Hartree–Fock and density functional studies on the structure and vibrational frequencies of quinone derived Schiff's base ligand

Abstract

The optimized structure of Schiff's base ligand 1-imino-(ethyl-2′pyridine)-2-hydroxy naphthoquinone 1 and its anion have been obtained from the ab initio Hartree–Fock and the hybrid density functional methods using the Dunning–Huzinaga double zeta basis set. For 1, the syn and anti conformers have been obtained as the local minima on the potential energy surface with the syn conformer as more stable than the anti conformer due to intramolecular hydrogen bonding. The stabilization energy for the syn conformer turns out to be 23.7 kJ mol −1 from the Hartree–Fock theory whereas the hybrid density functional method predicts this to be 39.8 kJ mol −1. Hartree–Fock calculated vibrational frequencies of the lowest energy conformer are in good agreement with those observed experimentally. On protonation of the anion the new band at 1550 cm −1 has been noted for the syn conformer. This vibration assigned to C–C stretching coupled with C–O–H bending corresponds 1567 cm −1 in the observed infrared spectrum.