The branched ionic liquids (ILs) 1-(iso-alkyl)-3-methylimidazolium bis­[(trifluoromethane)­sulfonyl]­amide ([(N – 2)­mC N‑1C1im]­[NTf2] with N = 3–7) were synthesized and their physicochemical properties characterized and compared with the properties of linear ILs 1-(n-alkyl)-3-methylimidazolium bis­[(trifluoromethane)­sulfonyl]­amide ([C N C1im]­[NTf2] with N = 3–7). For N = 4–7, the density of the branched IL [(N – 2)­mC N–1C1im]­[NTf2] is the same as that of its linear analogue [C N C1im]­[NTf2] within the standard uncertainty of the measurements. In the case of the N = 3 [1mC2C1im]­[NTf2]/[C3C1im]­[NTf2] pair, the density of the branched IL is 0.13% higher than that of the linear IL. For a branched/linear IL pair with a given N, the glass transition temperature T g, melting temperature T m, and viscosity η are higher for the branched IL than for the linear IL. [2mC3C1im]­[NTf2] is an exception in that its T m is lower than that of [C4C1im]­[NTf2]. Moreover, the viscosity of [2mC3C1im]­[NTf2] is anomalously higher than what would be predicted based on the trend of the other branched ILs. These trends in the viscosities of the linear and branched ILs are consistent with recent molecular dynamics simulations. Thermal gravimetric analysis indicates that linear ILs are thermally more stable than branched ILs. Pulsed-gradient spin–echo (PGSE) NMR diffusion measurements show that the self-diffusion coefficients of the ions vary inversely with the viscosities according to the Stokes–Einstein (SE) equation. The hydrodynamic radii of the cations and anions of linear ILs calculated from the SE equation however are consistently higher than those of the corresponding branched ILs.

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The intermolecular dynamics of dilute solutions of CS2 in 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([CnC1im][NTf2] for n = 1-4) were studied at 295 K using femtosecond optical Kerr effect (OKE) spectroscopy. The OKE spectra of the CS2/ionic liquid (IL) mixtures were analyzed using an additivity model to obtain the CS2 contribution to the OKE spectrum from which information about the intermolecular modes of CS2 in these mixtures was gleaned. The intermolecular spectrum of CS2 in these mixtures is lower in frequency and narrower than that of neat CS2, as found previously for CS2 in [C5C1im][NTf2]. Moreover, a dependence of the spectra on alkyl chain length is observed that is attributed to the interplay between electrostatic and dispersion interactions. The surprising result in this study is the solubility of CS2 in [C1C1im][NTf2], which involves the interaction of a nonpolar nonaromatic molecular solute and only the charged groups of the IL. We propose that the solubility of CS2 in [C1C1im][NTf2] is determined by three favorable factors - (1) large polarizability of the solute molecule; (2) small size of the solute molecule; and (3) low cohesive energy in the high-charge density regions of the IL.

The goal of this study was to evaluate the effectiveness of organic chemistry textbooks in developing student representational competence skills with eight representations of molecular structure (Lewis structures, Kekulé structures, condensed structures, electrostatic potential maps, skeletal structures, dash–wedge diagrams, Newman projections, and chair conformations). Five commonly used organic chemistry textbooks in the United States were deductively coded with Kozma and Russell’s representational competence framework. The analyses focused on identifying representational competence skills that are taught for each type of representation, as well as how consistently these skills are taught across text, worked examples, and practice problems within each textbook. We found that more representational competence skills are taught for some representations rather than others. In addition, all five textbooks may promote foundational representational competence skills, such as the ability to interpret, translate, and generate representations, but may fail to support learners in developing higher-level metarepresentational skills. Generally, more skills are taught in text, in comparison to the number of skills that are scaffolded in worked examples and assessed in practice problems. This means that the textbooks introduce various skills but do not provide as much support for students to develop and practice these skills. Finally, worked examples of some textbooks provide much more scaffolded explanations than others, allowing for a different amount of skill-building support.