Vibrational spectral investigations and density functional theory study of 4-Formylbenzoic acid

• DFT calculations for 4-FBA reproduces experimental vibrational wavenumbers excellently.
• Molecular geometry optimization exposes the planarity of 4-FBA molecule.
• NBO analysis reveals hyperconjugative interactions and stabilization of molecules.
• Shifting in CO stretching wavenumber is due to OH⋯O hydrogen bonding.
• Lowering of HOMO–LUMO energy gap indicates the possibility of biological activity.

An accurate assignment of the vibrational spectra of 4-Formylbenzoic acid in solid state was carried out. For this purpose density functional calculations (DFT) were performed to clarify wavenumber assignments of the experimentally observed bands for the first time. A scaling of the wavenumbers was carried out to improve the calculated values. Good reproduction of the experimental wavenumbers is obtained and the % error is very small in the majority of cases. The NBO analysis was carried out, and it reveals hyper conjugative interaction, ICT and stabilization of molecules.

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