The IR and Raman spectra and conformations of the ionic liquid 1-ethyl-3-methyl-1H-imidazolium tetrafluoroborate, [EMIM] [BF 4 ] (6), were analyzed within the framework of scaled quantum mechanics (SQM). It was shown that SQM successfully reproduced the spectra of the ionic liquid. The computations revealed that normal modes of the EMIM ¥ BF À 4 ion pair closely resemble those of the isolated ions EMIM and BF À 4 , except for the antisymmetric BF stretching vibrations of the anion, and the out-of-plane and stretching vibrations of the HÀC(2) moiety of the cation. The most plausible explanation for the pronounced changes of the latter vibrations upon ion-pair formation is the H-bonding between HÀC(2) and BF À 4 . However, these weak H-bonds are of minor importance compared with the Coulomb interactions between the ions that keep them closely associated even in dilute CD 2 Cl 2 solutions. According to the −gas-phase× computations, in these associates, the BF À 4 anion is positioned over the imidazolium ring of the EMIM cation and has short contacts not only with the HÀC(2) of the latter, but also with a proton of the MeÀN(3) group.

The solubility of H(2)S in a series of 1-butyl-3-methylimidazolium ([bmim](+)) based ionic liquids (ILs) with different anions, chloride, tetrafluoroborate ([BF(4)](-)), hexafluorophosphate ([PF(6)](-)), triflate ([TfO](-)), and bis(trifluoromethyl)sulfonylimide ([Tf(2)N]-), and in a series of [Tf(2)N] ILs with different cations, i.e., N-alkyl-N'-methylimidazolium, 2-methyl-N-methyl-N'-alkyimidazolium, N-alkylpyridinium, N-butyl-N-methylpyrrolidinium, and N-alkyl-N,N-dimethyl-N-(2-hydroxyethyl)ammonium has been determined using medium-pressure NMR spectroscopy. The observed solubilities are significantly higher than those reported for many other gases in ILs, suggesting the occurrence of specific interactions between H2S and the examined ILs. Quantum chemical calculations have been used to investigate at a molecular level the interaction between H2S and the [bmim](+)-based ILs.

The Diels-Alder reaction between cyclopentadiene and methyl acrylate in ionic liquids has been studied in detail. The effect of contamination of the ionic liquids by common impurities, viz. sodium and chloride ions, and water, on the selectivity has been investigated. The presence of high concentrations of chloride was found to decrease the selectivity. Anion and, in particular, cation effects have been investigated using an extensive series of air-stable room temperature ionic liquids, and kinetic parameters have been determined. It has been found that strongly interacting groups, particularly electrophilic moieties on the cation, accelerate the formation of the endo products. Substrate solubility intimately connected to the selectivity was found to be mainly anion dependent. An NMR-based solvent parameter scale and semi-empirical models are used to analyse the results and provide a tool for the prediction of selectivities in ionic liquids.

DFT methods in combination with NMR spectroscopy are used to investigate possible variants of the molecular structure of the ion pairs of the ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM][BF(4)], in dichloromethane. According to the computations of the chemical shifts, experimental NMR spectra can be rationalized by an equilibrium between ca. 70-80% of structures with the anion positioned near to the C2 atom of the imidazolium ring and ca. 20-30% of structures with the anion close to the C5 and/or C4 atoms. The content of the latter structures, according to the computed Gibbs free energies, does not exceed 10%. Both the computations and the experimental NMR data suggest that the ratio of the two above-mentioned types of structures of the imidazolium-based ILs is influenced by the concentration/polarity of their dichloromethane solutions.

The effect of pressure on the Diels-Alder reaction was examined in room temperature ionic liquids, followed by high-pressure FT-IR spectroscopy using pressures up to 150 MPa. Pressure enhances the kinetic sensitivity of the reaction. The kinetic effect of fluorophobic interactions was examined using ionic liquids with fluorous cations. Ionic liquids in combination with ZnI 2 as a Lewis acid catalyst were also studied under high pressure.

The Diels–Alder reaction has been examined in room temperature ionic liquids with high molar concentrations of Lewis acids under various conditions. A molar ratio of 10% catalyst gave a large increase in the selectivity and the yield of the reaction. The effect of catalysts on reaction rates was also examined under 100 MPa of pressure which leads to modest improvements in reaction rates. Ultrasound and microwave dielectric heating were also shown to improve the rate and, to a minor extent, selectivity of the examined reactions. Copyright © 2008 John Wiley & Sons, Ltd.

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