Polarity and hydrogen-bond-donor strength for some ionic liquids: Effect of alkyl chain length on the pyrrolidinium cation

Several ionic liquids were synthesized to investigate the influence of alkyl chain length and functional group attached to the cation on polarity and on three Kamlet–Taft parameters. Results are reported for polarity, dipolarity/polarizability, hydrogen-bond-donating acidity, and hydrogen-bond- accepting basicity in the range 25–65 °C. A long alkyl chain (1-octyl) on the pyrrolidinium cation leads to high polarity and high hydrogen-bond-donating acidity. At 25 °C, the hydrogen-bond-donating acidity for 1-methyl-1-octyl pyrrolidinium bis(trifluoromethansulfonyl)imide is close to that for water.