Interaction between the π-System of Toluene and the Imidazolium Ring of Ionic Liquids: A Combined NMR and Molecular Simulation Study

The solute−solvent interactions and the site−site distances between toluene and ionic liquids (ILs) 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide [BMMIm][NTf₂] and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIm][NTf₂] at various molar ratios were determined by NMR experiments (1D NMR, rotating-frame Overhauser effect spectroscopy (ROESY)) and by molecular simulation using an atomistic force field. The difference in behavior of toluene in these ILs has been related to the presence of H-bonding between the C₂−H and the anion in [BMIm][NTf₂] generating a stronger association (>20 kJ·mol⁻¹) than in the case of [BMMIm][NTf₂]. Consequently, toluene cannot cleave this H-bond in [BMIm][NTf₂] which remains in large aggregates of ionic pairs. However, toluene penetrates the less strongly bonded network of [BMMIm][NTf₂] and interacts with [BMMIm] cations.