Vibrational spectral analysis, computation of thermodynamic functions for various temperatures and NBO analysis of 2,3,4,5-tetrachlorophenol using ab initio HF and DFT calculations

摘要

FT-IR and FT-Raman spectra of 2,3,4,5-tetrachlorophenol (TCP) have been recorded in the regions 4000-400 cm-1 and 3500-100 cm-1 respectively. The total energy calculations of TCP were tried for the possible conformers. The molecular structure, geometry optimization, vibrational frequencies were obtained by the ab initio and DFT levels of theory (B3LYP and B3PW91) with the standard basis sets, 6-311++G(d, p) and 6-311+G(d, p) for C1 and C2 conformers. The harmonic frequencies were calculated and the scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and the calculated frequencies are found to be in good agreement. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The thermodynamic functions (heat capacity, entropy, vibrational partition function and Gibbs energy) from spectroscopic data by statistical methods were obtained for the range of temperature 100-1000 K. The polarizability, first hyperpolarizability, anisotropy polarizability invariant has been computed using quantum chemical calculations. The chemical parameters were calculated from the HOMO and LUMO values.