Conformers of 1-alkyl-3-methylimidazolium cations contained in ionic liquids

I&EC 129

José Nuno A. Canongia Lopes, jnlopes@ist.utl.pt, Centro de Química Estrutural, Instituto Superior Técnico, Av. Rovisco Pais, 1049 001 Lisboa, Portugal and Agílio A. H. Pádua, agilio.padua@univ-bpclermont.fr, Laboratoire de Thermodynamique des Solutions et des Polymères, CNRS/Université Blaise Pascal, 24, avenue des Landais, 63177 Aubière, France.
The development in the last years of molecular models for ionic liquids was received with great interest by the scientific community. However, the validation of those models against experimental data remains a critical issue to the present day. In a recent article [JPCA 109, 8976 (2005)] it was demonstrated using Raman spectroscopy data and quantum chemical calculations that the 1-ethyl-3-ethylimidazolium cation contained in different ionic liquids exists as a mixture of two main conformers. These results confirmed the soundness of the approximations used when developing a systematic molecular force-field for ILs by the authors of this presentation [JPCB 108, 2038 (2004)]. In another recent publication [JPCB 109, 19018 (2005)], the existence of conformers of 1-butyl- and 1-hexyl-3-methylimidazolium cations was also demonstrated. In this presentation we will validate our force-field against the spectroscopic and ab initio data by confronting them with condensed phase dihedral distribution results obtained from MD simulations.