Comparative vibrational spectroscopic studies, HOMO–LUMO and NBO analysis of 5,7-dibromo-8-hydroxyquinoline and 5,7-dichloro-8-hydroxyquinoline based on Density Functional Theory

Comparative studies of the Raman and infrared spectra, the geometry, frequency and intensity of the vibrational bands of 5,7-dibromo-8-hydroxyquinoline (DBHQ) and 5,7-dichloro-8-hydroxyquinoline (DCHQ) were obtained by using Density Functional Theory calculations (DFT) with B3LYP functional and 6-311++G** basis set. The effects of bromine and chlorine substituents on the vibrational frequencies of 8-hydroxyquinoline have been investigated. The assignments have been proposed with aid of the results of normal coordinate analysis. Coupling of vibrations have been determined by calculating potential energy distributions (PEDs). The molecular stability and bond strength was investigated by applying the Natural Bond Orbital analysis (NBO). The other molecular properties like Mulliken population analysis, thermodynamic functions and polarizabilities of the title compounds have been reported. The calculated HOMO and LUMO energies show that charge transfer occur in the molecules. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential (ESP).