DFT Analysis of the Gas Phase Interactions of Choline Chloride with Urea

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Résumé

Choline chloride and urea interact to form a Deep Eutectic Solvent widely used as a green solvent in several
applications such as electrochemistry, chemical substance separation and reactions. We searched for the equilibrium
geometries, charges distributions of model compounds of their respective associated complexes of 1:1, 1:2 and 1:3 ratios. The
calculated interaction energies indicate that several stable conformers of the DES may form and coexist in the solvent
medium. Beside coulombic interactions, NBO analysis shows that the through bond interactions between occupied orbitals
and empty antibonding molecular orbitals contribute to spread the electronic charge and stabilize the systems. These
interactions involve mainly the lone pairs of the electronegative elements Cl, N and O so that H-bonds of the type C=O---H-O,
Cl---H-N, Cl---H-C and C=O---H- link the various neutral and ionic fragments in the model compounds of the solvent.
Calculated Wiberg bond indices revealed the partial covalent nature of these H-bonds.

Mots-clés

Density functional theory calculations, Choline chloride-urea compounds, Deep eutectic solvents, NBO analysis, H-bonds