Solvent Effects on the 1H‐NMR Chemical Shifts of Imidazolium‐Based Ionic Liquids

Abstract

AbstractThe 1H nuclear magnetic resonance (1H‐NMR) spectrum is a useful tool for characterizing the hydrogen bonding (H‐bonding) interactions in ionic liquids (ILs). As the main hydrogen bond (H‐bond) donor of imidazolium‐based ILs, the chemical shift (δH2) of the proton in the 2‐position of the imidazolium ring (H2) exhibits significant and complex solvents, concentrations and anions dependence. In the present work, based on the dielectric constants (ϵ) and Kamlet‐Taft (KT) parameters of solvents, we identified that the δH2 are dominated by the solvents polarity and the competitive H‐bonding interactions between cations and anions or solvents. Besides, the solvents effects on δH2 are understood by the structure of ILs in solvents: 1) In diluted solutions of inoizable solvents, ILs exist as free ions and the cations will form H‐bond with solvents, resulting in δH2 being independent with anions but positively correlated with βS. 2) In diluted solutions of non‐ionzable solvents, ILs exist as contact ion‐pairs (CIPs) and H2 will form H‐bond with anions. Since non‐ionizable solvents hardly influence the H‐bonding interactions between H2 and anions, the δH2 are not related to βS but positively correlated with βIL.