Search

We characterize the double‐faced nature of hydrogen bonding in hydroxy‐functionalized ionic liquids by means of neutron diffraction with isotopic substitution (NDIS), molecular dynamics (MD) simulations, and quantum chemical calculations. NDIS data are fit using the empirical potential structure refinement technique (EPSR) to elucidate the nearest neighbor H⋅⋅⋅O and O⋅⋅⋅O pair distribution functions for hydrogen bonds between ions of opposite charge and the same charge. Despite the presence of repulsive Coulomb forces, the cation–cation interaction is stronger than the cation–anion interaction. We compare the hydrogen‐bond geometries of both "doubly charged hydrogen bonds" with those reported for molecular liquids, such as water and alcohols. In combination, the NDIS measurements and MD simulations reveal the subtle balance between the two types of hydrogen bonds: The small transition enthalpy suggests that the elusive like‐charge attraction is almost competitive with conventional ion‐pair formation. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Certain protic ionic liquids (PILs) are potentially low‐cost, high‐efficiency solvents for the extraction and processing of aromatic compounds. To understand the key design features of PILs that determine solubility selectivity at the atomic level, neutron diffraction was used to compare the bulk structure of two PILs with and without an aromatic solute, guaiacol (2‐methoxyphenol). Guaiacol is a common lignin residue in biomass processing, and a model compound for anisole‐ or phenol‐based food additives and drug precursors. Although the presence of amphiphilic nanostructure is important to facilitate the dissolution of solute nonpolar moieties, the local geometry and competitive interactions between the polar groups of the cation, anion, and solute are found to also strongly influence solvation. Based on these factors, a framework is presented for the design of PIL structure to minimize competition and to enhance driving forces for the dissolution of small aromatic species. Non‐stop protic cabaret: To understand the key design features of protic ionic liquids (PILs) that determine solubility selectivity at the atomic level, neutron diffraction is used to compare the bulk structure of two PILs with and without an aromatic solute, guaiacol. The local geometry and competitive interactions between the polar groups of the cation, anion, and solute are found to strongly influence solvation. [ABSTRACT FROM AUTHOR]