Abstract
We investigate the conformers of the N-methoxyethyl-N-methylpyrrolidinium (PYR1(2O1)) and N-ethoxyethyl-N-methylpyrrolidinium (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).
Highlights
IntroductionThe large variety of possible anions and cations allows tailoring their physiochemical properties, such as viscosity, electrical conductivity, melting point, or glass transition temperature
Ionic liquids are salts with melting points lower than 100∘C
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
Summary
The large variety of possible anions and cations allows tailoring their physiochemical properties, such as viscosity, electrical conductivity, melting point, or glass transition temperature. One of the most studied ILs is 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) It displays a rich phase diagram as a function of temperature [2]: on cooling it undergoes a glass transition around −85∘C; on subsequent heating, it is devitrified and enters an undercooled region; at. PYR14TFSI has been largely investigated by means of vibrational spectroscopy, aided by DFT calculations [3,4,5,6,7,8] Both the TFSI anion and PYR14 cation possess conformers, due to the flexibility of the chemical bonds. The two conformers are energetically separated by only 2.2 kJ mol−1
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