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

Abstract

We investigate the conformers of the N -methoxyethyl- N -methylpyrrolidinium ( P Y R 1 ( 2 O 1 ) ) and N -ethoxyethyl- N -methylpyrrolidinium ( P Y R 1 ( 2 O 2 ) ) ionic liquid cations by means of DFT calculations at the B3LYP/ 6 - 31 G ⁎ ⁎ 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 PYR 14 , 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 P Y R 1 ( 2 O 1 ) and P Y R 1 ( 2 O 2 ) than in the parent ion 1-butyl-1-methylpyrrolidinium (PYR 14 ).