Conformational stability, vibrational assignments of 2,3-dihydroxy benzaldehyde as supported by ab initio, hybrid density functional theory and normal coordinate analysis

FT-IR and FT-Raman spectra of 2,3-dihydroxybenzaldehyde (DHB) have been recorded in the regions 4000–400 cm−1 and 3500–100 cm−1, respectively. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) both B3LYP/6-31+G (d, p) and HF/6-31+G (d, p) basis sets combination. There are eight possible conformers (Cn, n = 1–8) for this molecule. The computational results identify the most stable conformer of DHB as the C6 form. The molecular structures, vibrational frequencies infrared intensities and Raman scattering activities were calculated. The spectroscopic and theoretical results are compared to the corresponding properties for DHB of C6 conformer. The optimized geometries and normal modes vibration obtained from DFT method are in good agreement with the experimental data. The formation of intermolecular hydrogen bond was investigated using NBO calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule and ESP contour map shows the electrophilic and nucleophilic region of the molecule.

► The optimized geometrical parameters of DHB were obtained by HF and B3LYP methods.
► Global minimum energy for eight conformers of DHB have been studied.
► Experimental spectra compared with theoretically simulated spectra of DHB..
► HOMO and LUMO analysis have been performed.
► Thermodynamic parameter has been performed.