Vibrational spectra, NLO analysis, and HOMO–LUMO studies of 2-chloro-6-fluorobenzoic acid and 3,4-dichlorobenzoic acid by density functional method

• Vibrational wave numbers and TED of CFBA and DCBA have been carried out.
• The assignments of most of the fundamentals are believed to be unambiguous.
• Mulliken’s charges, HOMO–LUMO and MEPS analysis were performed.
• Hyperpolarizability and several thermodynamic properties were performed.

The FTIR and FT-Raman spectra of 2-chloro-6-fluorobenzoic acid and 3,4-dichlorobenzoic acid have been recorded in the region 4000–400 cm−1 and 3500–50 cm−1, respectively. Utilizing the observed FTIR and FT-Raman data, a complete vibrational assignment and analysis of fundamental modes of the compounds were carried out. The optimized molecular geometries, vibrational frequencies, thermodynamic properties and atomic charge of the compounds were calculated by using density functional theory (B3LYP) method with 6-311+G and 6-311++G basis sets. The difference between the observed and scaled wave number values of most of fundamentals is very small. Unambiguous vibration assignment of all the fundamentals is made up the total energy distribution (TED). The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules. Besides, molecular electro static potential (MESP), Mulliken’s charge analysis, first order hyper polarizability and several thermodynamic properties were performed by the DFT method.

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