Molecular structure analysis and spectroscopic characterization of 5-ethyl-5-phenyl-1,3-diazinane-4,6-dione with experimental (FT-IR and FT-Raman) techniques and quantum chemical calculations

In this work, the FT-IR and FT-Raman spectra of 5-ethyl-5-phenyl-1,3-diazinane-4,6-dione have been recorded. The optimum molecular geometry, normal mode wavenumbers, infrared and Raman intensities, Raman scattering activities, corresponding vibrational assignments and Mullikan atomic charges were investigated with the help of HF and B3LYP(DFT) methods using 6-31G(d,p) basis set. The assignments of vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) following the scaled quantum mechanical force field (SQMFF) methodology. The stability of molecule has been analyzed by NBO analysis. The calculated HOMO and LUMO energies show that charge transfer interactions take place within the molecule. Finally, the Mulliken population analysis on atomic charges of the title compound has been calculated.

A complete vibrational analysis of 5-ethyl-5-phenyl-1,3-diazinane-4,6-dione is performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT) based on scaled quantum chemical approach. The calculated HOMO and LUMO energies show that charge transfer occur within the molecule. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.Figure optionsDownload as PowerPoint slideHighlights
► FT-IR and FT-Raman spectra of 5-ethyl-5-phenyl-1,3-diazinane-4,6-dione in the solid phase were recorded and analyzed.
► The optimized geometry and vibrational wavenumbers were computed using ab initio HF and DFT methods.
► The complete vibrational assignment and spectroscopic analysis have been carried out.
► The first order hyperpolarizability and HOMO, LUMO energy gap were theoretically predicted.
► The NBO analysis explained the intramolecular hydrogen bonding.