Molecular structure, tautomeric stability, protonation and deprotonation effects, vibrational, NMR and NBO analyses of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA) by quantum chemical calculations

• The structure, vibrational, electronic, NMR, NBO analysis of (DOIAA) was studied.
• PES scan results showed that the most stable conformer is the syn conformer.
• Tautomerism and the effect of solvent on the tautomeric equilibria were studied.
• Deprotonation enthalpies showed that N2 deprotonation site is more stable than N5.

This study represents the conformation, tautomeric stability, protonation and deprotonation effects, vibrational, electronic, NBO and NMR aspects of 2,4-Dioxoimidazolidine-5-acetic acid (DOIAA). Theoretical calculations were performed by ab initio HF and density functional theory (DFT)/B3LYP method using 6-311++G(d,p) basis sets. Tautomerism and the effect of solvent on the tautomeric equilibria in the gas phase and in different solvents were studied. The protonation and deprotonation effects on the reactivity and conformations of DOIAA were investigated. Electronic transitions were also studied and the most prominent transition corresponds to π → π*. Natural bond orbital (NBO) analysis was also carried out to find the intramolecular interactions and their stabilization energy. In DOIAA, the interaction between the lone pair donor orbital (n(LP1N5)) and the acceptor antibonding orbital π*(C6O7) reveals the strong stabilization energy of 224.9 kJ mol−1. Molecular electrostatic potential (MEP) was calculated to predict the reactive sites of the title compound. The NMR results indicated that the observed chemical shifts for NH, COOH protons of DOIAA not only depend on the structure of the molecule being studied but also on the nature of the solvent, concentration of the sample and the presence of the other exchangeable protons.

Conformation, tautomeric stability, vibrational, electronic, NMR, reactivity and structural aspects of DOIAA were studied in detail using DFT method and the results were also compared with the experimental value. PES scan results showed that the most stable conformer is the syn conformer. Tautomerism and the effect of solvent on the tautomeric equilibria for the predominant form in the gas phase and in selected solvents were studied. Results indicated that the tautomer T1 (di-keto form) was the most stable one. In addition, NPA atomic charges were also calculated for the T1 form. The proton affinity and deprotonation enthalpies of DOIAA were calculated at B3LYP/6-311++G(d,p) basis sets. The results indicate that the protonation on O7 site is found to be strongly favored over the O4 site. The lower frontier orbital energy gap illustrates the high reactivity of the title compound. NBO analysis results showed that the strong intramolecular interactions take place in DOIAA. The calculated 1H and 13C NMR chemical shifts of DOIAA were compared with the experimental data. The NMR results indicated that the observed chemical shifts for NH, COOH protons of DOIAA not only depend on the structure of the molecule being studied but also on the solvent used.Figure optionsDownload as PowerPoint slide