Symmetry vs. asymmetry – Enthalpic differences in imidazolium-based ionic liquids

Abstract Enthalpies of ionic liquids [CnCnIm][X] synthesis reactions were measured with help of differential scanning calorimetry. These results in combination with quantum-chemical calculations were used for estimation of vaporization enthalpies of symmetric imidazolium based ionic liquids with X = Cl, Br, and I. Vaporization enthalpies of the symmetric ([CnCnIm][X]) series were found to be systematically lower (of 5–8 kJ mol−1) in comparison with the corresponding asymmetric imidazolium-based ILs ([CnC1Im][X]). This energetic difference was attributed to the intensity of dispersion interactions.