FT-Raman and FTIR spectra, DFT investigation of the structure and vibrational assignment of mefenacet

• Electronegativity effect of neighbouring atoms shortens the CN bond lengths.
• IR and Raman spectra of mefenacet were analysed by SQM calculations.
• Lowering of CO stretching mode indicates the effect of intermolecular interaction.

FTIR and Raman spectral techniques were employed for the vibrational characterization of the herbicide mefenacet. The equilibrium geometry, various bonding features and harmonic vibrational wavenumbers were investigated with the help of density functional theory calculations. A detailed assignment of the vibrational spectra was made with the aid of theoretically predicted vibrational frequencies. Natural bond orbital analysis on mefenacet was carried out to reveal the nature of different interactions responsible for electron delocalization and the charge transfer between the orbitals (n → π∗, n → σ∗, π → π∗). Structural changes in the molecule due to the substitution of highly electronegative oxygen atom, conjugation and resonance effect were analyzed.