Quantum chemical studies on the molecular structure and vibrational spectra of some organic molecules based on density functional theory calculations

Abstract

newline The FT IR and FT Raman spectra of certain pharmaceutically industrially and biologically significant organic molecules have been recorded in the range 4000 500cm 1 All the observed vibrational bands of the compounds were assigned to the various modes of vibrations and discussed in comparison with the structurally similar molecules and theoretical values Optimized geometries of the molecules have been interpreted and compared with the reported experimental values The harmonic vibrational wavenumbers IR and Raman intensities were calculated at the same theory levels used in geometry optimization The vibrational frequencies are assigned with PED Potential Energy Distribution values The calculated frequencies are scaled and compared with experimental values. The scaled vibrational frequencies at DFT B3LYP 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 Molecular Electrostatic Potential MEP and Natural Bond Orbital NBO analysis were performed at various basis sets The correlation equations between heat capacities entropies enthalpy changes and temperatures were fitted by quadratic formula UV visible spectral analysis on some organic molecules have been researched by theoretical calculations Also in order to understand electronic transitions of the compound TD DFT calculations were made on electronic absorption spectra in gas phase and water The calculated frontier orbital energies absorption wavelengths and#955; oscillator strengths f and excitation energies E for gas phase and water are also illustrated for organic compounds All the analyses were predicted with the aid of experimental theoretical and graphical approaches newline newline