Primidone – An antiepileptic drug – characterisation by quantum chemical and spectroscopic (FTIR, FT-Raman, 1H, 13C NMR and UV–Visible) investigations

• FTIR, FT-Raman, NMR and UV–Visible spectra of antiepileptic drug were analysed.
• The phenyl group is planar while the heterocyclic ring possesses boat conformations.
• The coplanar CNC angle of N1 and N3 is 122.5° while the CCN for C4 and C6 is 114.3°.
• The frontier orbital energy gap (ELUMO − EHOMO) is found to be 6.152 eV.
• The nN→πCO∗ between nitrogen lone pair and C4O7 antibonding orbital has stabilisation 60.84 kJ/mol.

The solid phase FTIR and FT-Raman spectra of primidone were recorded in the regions 4000–400 cm−1 and 4000–100 cm−1, respectively. The vibrational spectra were analysed and the observed fundamentals were assigned and analysed. The experimental wavenumbers were compared with the theoretical scaled vibrational wavenumbers determined by DFT methods. The Raman intensities were also determined with B3LYP/6-31G(d,p) method. The total electron density and molecular electrostatic potential surface of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei) distribution. The HOMO and LUMO energies were measured. Natural bond orbital analysis of primidone has been performed to indicate the presence of intramolecular charge transfer. The 1H and 13C NMR spectra were recorded and the chemical shifts of the molecule were calculated.

The FT-IR, FT-Raman, 1H, 13C and NMR spectral measurements of an antiepileptic drug primidone and complete assignments of the observed spectra have been elaborated. DFT calculations have been performed and the structural parameters of the compound were determined from the optimised geometry with 6-31G(d,p), 6-311++G(d,p), cc-pVTZ and LanL2dz basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR and Raman intensities. The influences of various factors regarding the stability and the conformers have been discussed. A detailed bond pair–band pair and bond pair–lone pair interaction analysis was carried out.Figure optionsDownload as PowerPoint slide