Molecular structure, spectroscopic (FT-IR, FT-Raman), NBO and HOMO-LUMO analyses, computation of thermodynamic functions for various temperatures of 2, 6-dichloro-3-nitrobenzoic acid.

The FT-IR and Raman spectra of 2, 6-dichloro-3-nitrobenzoic acid (DCNBA) have been recorded and analyzed. The equilibrium geometry, various bonding and harmonic vibrational wavenumbers have been calculated with the help of density functional theory (DFT/B3LYP/cc-pvdz/6-311++G(d,p)) method. The optimized geometrical parameters obtained by B3LYP/6-311++G(d,p) method show good agreement with experimental X-ray data. Most of the vibrational modes are observed in the expected range. The Mulliken population analysis shows the interactions of C-N-O···H-C and C-O···H-C. The most possible interaction is explained using natural bond orbital (NBO) analysis. The effects of molecular association through O-H···O hydrogen bonding have been described by the single dimer structure. The strengthening and polarization of the C=O bond increases due to the degree of conjugation. HOMO-LUMO energy and the thermodynamic parameters are also evaluated. The thermodynamic functions (heat capacity, internal heat energy, Gibbs energy and entropy) from spectroscopic data by statistical methods were obtained for the range of temperature 100-1000 K.