Spectroscopic analysis of cinnamic acid using quantum chemical calculations

• Monomer and dimer structures of cinnamic acid were examined.
• Spectroscopic analysis was characterized by FT-IR, FT-Raman and NMR techniques.
• MSP and Mulliken charge analysis of the compound were studied.
• HOMO and LUMO energies and UV of the molecule were calculated.

In this present study, FT-IR, FT-Raman, 13C NMR and 1H NMR spectra for cinnamic acid have been recorded for the vibrational and spectroscopic analysis. The observed fundamental frequencies (IR and Raman) were assigned according to their distinctiveness region. The computed frequencies and optimized parameters have been calculated by using HF and DFT (B3LYP) methods and the corresponding results are tabulated. On the basis of the comparison between computed and experimental results assignments of the fundamental vibrational modes are examined. A study on the electronic and optical properties; absorption wavelengths, excitation energy, dipole moment and frontier molecular orbital energies, were performed by HF and DFT methods. The alternation of the vibration pattern of the pedestal molecule related to the substitutions was analyzed. The 13C and 1H NMR spectra have been recorded and the chemical shifts have been calculated using the gauge independent atomic orbital (GIAO) method. The Mulliken charges, UV spectral analysis and HOMO–LUMO analysis of have been calculated and reported. The molecular electrostatic potential (MEP) was constructed.

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