DFT studies of structure and vibrational spectra of 4-benzylidene-1-phenyl-2-selenomorpholino-1H-imidazol-5(4H)-one and its derivatives

• The Raman and IR spectra of six 1H-imidazol-5(4H)-one derivatives are measured.
• The geometries and vibrational spectra are studied by DFT at B3LYP/6-31G(d) level.
• The influence of substituent on IR and Raman spectrum is discussed.
• The effect of intermolecular interaction on vibrational spectrum is studied.

The Raman spectra and FT-IR spectra of 4-benzylidene-1-phenyl-2-selenomorpholino-1H-imidazol-5(4H)-one and its derivatives have been measured and their ground-state geometries and vibrational spectra are studied by DFT at B3LYP/6-31G(d) level. Comparing the optimized geometries of compounds 1-6, we find that different substituent and substitution site on benzene rings result in very small changes on the imidazoline skeleton, the changes on bond length are within 0.005 Å and on bond angle are within 0.5°. Calculated spectra are well consistent with the experimental one and the deviations are smaller than 30cm-1. The influence of substituent on IR and Raman spectrum must not be neglected. Electron-withdrawing chlorine atom makes the stretching vibration of carbonyl group shift 4–16 cm−1 towards higher wavenumber, but electron-donating methoxyl group and dioxole group make it shift 6–10 cm−1 in IR and 9–13 cm−1 in Raman spectrum towards lower wavenumber, respectively. Dioxole substitution makes the CC stretching vibration of phenyl shift to a higher position at 1617–1618 cm−1. The influence of intermolecular weak interaction on vibrational spectrum is studied by two models (dimer and monomer inclusion van del Waals correction). Dimer model presents a better accuracy, but van del Waals correction on B3LYP hybrid function does not produce a significant change on accuracy in this system.

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