Symmetry Breaking in Chiral Ionic Liquids Evidenced by Vibrational Optical Activity

Abstract

Ionic liquids (ILs) are receiving increasing interest for their use in synthetic laboratories and industry. Being composed of charged entities, they show a complex and widely unexplored dynamic behavior. Chiral ionic liquids (CILs) have a high potential as solvents for use in asymmetric synthesis. Chiroptical methods, owing to their sensitivity towards molecular conformation, offer unique possibilities to study the structure of these chiral ionic liquids. Raman optical activity proved particularly useful to study ionic liquids composed of amino acids and the achiral 1-ethyl-3-methylimidazolium counterion. We could substantiate, supported by selected theoretical methods, that the achiral counterion adopts an overall chiral conformation in the presence of chiral amino acid ions. These findings suggest that in the design of chiral ionic liquids for asymmetric synthesis, the structure of the achiral counter ion also has to be carefully considered.

Recent Trends in Chiroptical Spectroscopy: Theory and Applications of Vibrational Circular Dichroism and Raman Optical Activity

“…Ouveley et al. used VCD and ROA to study alanine, valine or leucine, with 1‐ethyl‐3‐methylimidazolium as a counterion (Figure ) . Interestingly, VCD does not provide many characteristic features to distinguish the three compounds; more marker bands can be observed in the ROA spectrum.…”

“…Ouveley et al used VCD and ROA to study alanine, valine or leucine, with 1-ethyl-3-methylimidazolium as a counterion (Figure 5). [140] Interestingly, VCD does not provide many characteristic features to distinguish the three compounds; more marker bands can be observed in the ROA spectrum. The 1-ethyl-3methylimidazolium heavily contributes to the Raman and ROA spectra in 300-400 cm À 1 and 1300-1600 cm À 1 , that means that it also becomes chiral in the liquid.…”

“…Raman, IR, ROA and VCD spectra of three ionic liquids, leucine, valine or alanine, with 1-ethyl-3-methylimidazolium counterion. Reproduced from ref [140]. with permission from Wiley-VCH.…”

Clara‐Immerwahr‐Preis: S. Luber / Alwin‐Mittasch‐Preis: X. Bao und D. J. Cole‐Hamilton / Jochen‐Block‐Preis: M. Sanchez‐Sanchez / In die Berlin‐Brandenburgische Akademie der Wissenschaften gewählt: B. Albert / Wiley–CST Green Chemistry Award: P. Thamyongkit

“…Dazu zählt die genaue Untersuchung komplexer Flüssigkeiten und funktioneller Moleküle in der Gasphase und auf Oberflächen, mit der künstlichen, durch Sonnenlicht getriebenen Wasserspaltung als besonderem Schwerpunkt. Sie ist Coautorin einer Arbeit in der Angewandten Chemie über chirale ionische Flüssigkeiten …”

Raman Optical Activity Spectra from Density Functional Perturbation Theory and Density-Functional-Theory-Based Molecular Dynamics

“…50,[57][58][59][60] Very recently, VCD spectra obtained from DFT-based MD have been presented as well. 61 In the framework of ROA spectroscopy, (classical or DFT-based) MD has solely been employed to sample solute-solvent clusters 19,39,[62][63][64][65][66][67] and a ionic liquid, 68 in this way providing input model structures for static calculations.…”