Molecular structure, vibrational spectroscopic and HOMO, LUMO studies of 4-nitroaniline by density functional method

20-30Quantum mechanical calculations of energies, geometries and vibrational wavenumbers of 4-nitroaniline (4NA) were carried out by using Density functional theory (DFT /B3LYP/6-311++G(d,p)/ CC-pvdz / Aug-cc-Pvdz) method. The optimized geometrical parameters obtained by B3LYP method show good agreement with experimental X-ray data. The best level of theory in order to reproduce the experimental wavenumbers is B3LYP method with the 6-311++G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. A detailed interpretation of the infrared spectra of 4NA was also reported. The calculated HOMO and LUMO energies show that charge transfer occurs in the molecule. The theoretical spectrogram for FTIR and FT-Raman spectra of the title molecule have been constructed

Molecular structure and vibrational spectra of 2-chlorobenzoic acid by density functional theory and <i>ab-initio</i> Hartree-Fock calculations

248-258The structure, harmonic frequencies and vibrational mode assignments for 2-chlorobenzoic acid (2CBA) monomer are calculated using HF and DFT methods employing the 6-311++G(d,p) basis set. The results of the molecular structure and vibrational frequencies obtained on the basis of calculations are presented and critically compared with the experimental IR data recorded in gas phase. The Raman and IR spectral data of 2-chlorobenzoic acid (2CBA) obtained in solid phase have also been included. The normal mode analysis has been carried out for all the modes. Most of the modes have wavenumbers in the expected range. The experimental spectra also coincide satisfactorily with those of theoretically constructed spectrograms