The Effect of C4H and C5H on the Microstructure of Aqueous Solutions of 1-Alkyl-3-methylimidazolium Tetrafluoroborate Ionic Liquids

As is well-known, the C2H proton of 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4) and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4) has a strong ability to form hydrogen bonds. The purpose of this work is to evaluate the effect of the interactions of the C4H and C5H protons on the microstructure of [Emim]BF4 and [Bmim]BF4 with water by using H-1 NMR spectroscopy. The differences between the relative H-1 NMR chemical shifts of C2H, C4H, and C5H and between the interaction-energy parameters obtained from these chemical shifts are minor, thus suggesting that the interactions of C4H and C5H may have a considerable effect on the microstructure. To confirm this, the viscosities of the systems are estimated by using the interaction-energy parameters obtained from the H-1 NMR chemical shifts of the three studied aromatic protons and water, showing that the interactions of C4H and C5H also play an important role in the microstructure.