A Computational and Experimental Study of the Conformers of Pyrrolidinium Ionic Liquid Cations Containing an Ethoxy Group in the Alkyl Side Chain

We investigate the conformers of the N-methoxyethyl-N-methylpyrrolidinium (PYR1(2O1)) and N-ethoxyethyl-Nmethylpyrrolidinium (PYR1(2O2)) ionic liquid cations by means of DFT calculations at the B3LYP/6-31G∗∗ level and we calculate their infrared vibration frequencies. The comparison with the absorbance spectra of two ionic liquids containing these ions indicates good performance of such a combination of theory and basis set.The lowest energy conformer of each pyrrolidinium cation displays equatorial-envelope geometry; however, in contrast with the prototypical PYR14, the main alkyl side chain is not in an all-trans configuration, but it tends to be bent. Moreover, calculations indicate that the LUMO orbital extends more along the alkyl side chain in PYR1(2O1) and PYR1(2O2) than in the parent ion 1-butyl-1-methylpyrrolidinium (PYR14).