Synthesis and spectroscopic properties of symmetrical ionic liquids based on (−)-menthol

The diastereotopic protons in the 1H NMR were thoroughly described. Moreover, the 1H NMR and 13C NMR spectra indicated notable differences in the chemical shifts depending on the anion used. Comparing the differences between values of the chemical shifts, the anions were ordered according to their increasing shielding capacities. The changing of the electron density surrounding the imidazolium ring was discussed.