Conformational analysis, infrared/Raman spectral assignment, and electronic structural studies of 1,3-dimethyl-2-imidazolidinone using quantum chemical calculations

Abstract

The conformational behavior of 1,3-Dimethyl-2-imidazolidinone (C5H10N2O; DMI) was investigated by quantum chemical calculations and vibrational (IR and Raman) spectral analysis. Ab initio (MP2) and DFT (B3LYP and ωB97XD) methods combined with the 6–311++G (d,p) and aug-cc-pVTZ basis sets were used. Aided by computational outcomes, the twist form (C2) was identified to be the most stable DMI conformer while the transition state planar assumption with C2v symmetry was higher than the twist conformer by 1.5–4.24 kcal/mol. In addition, the envelope form (Cs) was converged close to the planar form after allowing the structural parameters to relax with no constraints on the dihedral angles; therefore, it is not a minimum on the potential energy surface. The observed infrared and Raman spectral data are consistent with C2 molecular symmetry for DMI; therefore, confident vibrational spectral interpretations are reported herein supported by normal coordinate analysis and potential energy distributions (PEDs). The twist-to-planar energy barrier of DMI was predicted owing to the ring puckering using a two-variable scan of the potential energy surface at the B3LYP/6–311++G (d,p) level of theory. Finally, the OVGF and P3 calculations were performed for the twist conformer to predict the vertical ionization energies (IEs) and their corresponding outer-valence HOMOs. The reported gas-phase UV photoelectron spectrum was precisely interpreted. All results were analyzed herein and compared to similar molecules whenever appropriate.