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