FT IR and FT Raman Spectral Analysis and Scaled Quantum Mechanical calculations of certain active Benzene Pyridine and Naphthalene derivatives

Abstract

In the present study, the FT-IR and FT-Raman spectra of certain pharamaceutically, industrially and biologically active benzene, pyridine and naphthalene derivatives (totally eight molecules) have been recorded in the range 4000 cm-1 50 cm-1. All the observed vibrational bands of the compounds are assigned to the various modes of vibrations and discussed in comparison with the structurally similar molecules and theoretical values. All the optimized structural parameters have been calculated by HF, MP2 and DFT methods with different basis sets. Optimized geometries of the molecues have been interpreted and compared with the reported experimental values. The harmonic vibrational wavenumbers, IR and Raman intensities are calculated at the same theory levels used in geometry optimization. The vibrational frequencies are assigned with TED (Total Energy Distribution) values. The calculated frequencies are scaled and compared with experimental values. The scaled vibrational frequencies at B3LYP (DFT) method with higher order basis set seem to coincide with the experimentally observed values with acceptable deviations. Various Scaled Quantum Mechanical approaches helped this study to identify the structural and symmetry properties of the presently taken molecules. The impacts of substitutions on structure, frequency and other molecular properties in three different rings were studied eleborabtely. The correlation equations between heat capacities, entropies, enthalpy changes and temperatures were fitted by quadratic formulas. The Frontier Molecular Orbital analysis was carried out in order to identify the charge transfer interactions taking place within the molecule. UV-VIS spectral analyses on some complicated molecules of naphthalene and pyridine derivatives have been researched by theoretical calculations. Also, In order to understand electronic transitions of the compound, TD-DFT calculations on electronic absorption spectra in gas phase and solvent (DMSO and Chloroform) were performed.