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 (C 5 H 10 N 2 O; 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 ( C 2 ) was identified to be the most stable DMI conformer while the transition state planar assumption with C 2v symmetry was higher than the twist conformer by 1.5–4.24 kcal/mol. In addition, the envelope form ( C s ) 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 C 2 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.