Deuterium Kinetic Isotope Effects in Microsolvated Gas-Phase E2 Reactions

This work describes the first experimental studies of deuterium kinetic isotope effects (KIEs) for the gas-phase E2 reactions of microsolvated systems. The reactions of F−(H2O)n and OH−(H2O)n, where n = 0, 1, with (CH3)3CX (X = Cl, Br), as well as the deuterated analogs of the ionic and neutral reactants, were studied utilizing the flowing afterglow-selected ion flow tube technique. The E2 reactivity is found to decrease with solvation. Small, normal kinetic isotope effects are observed for the deuteration of the alkyl halide, while moderately inverse kinetic isotope effects are observed for the deuteration of the solvent. Minimal clustering of the product ions is observed, but there are intriguing differences in the nature and extent of the clustering process. Electronic structure calculations of the transition states provide qualitative insight into these microsolvated E2 reactions

Gas-Phase Reactions of Microsolvated Fluoride Ions: An Investigation of Different Solvents

The gas-phase reactions of F^–(DMSO), F^–(CH₃CN), and F^–(C₆H₆) with <i>t</i>-butyl halides were investigated. Reaction rate constants, kinetic isotope effects, and product ion branching ratios were measured using the flowing afterglow selected ion flow tube technique (FA-SIFT). Additionally, the structure of F^–(DMSO) was investigated both computationally and experimentally, and two stable isomers were identified. The reactions generally proceed by elimination mechanisms; however, the reaction of F^–(C₆H₆) with <i>t</i>-butyl chloride occurs by a switching mechanism. These reactions are compared to previous studies of microsolvated reactions of <i>t</i>-butyl halides where the solvent molecules were polar, protic molecules

Reactions of Ions with Ionic Liquid Vapors by Selected-Ion Flow Tube Mass Spectrometry

Room-temperature ionic liquids exert vanishingly small vapor pressures under ambient conditions. Under reduced pressure, certain ionic liquids have demonstrated volatility, and they are thought to vaporize as intact cation−anion ion pairs. However, ion pair vapors are difficult to detect because their concentration is extremely low under these conditions. In this Letter, we report the products of reacting ions such as NO⁺, NH₄⁺, NO₃⁻, and O₂⁻ with vaporized aprotic ionic liquids in their intact ion pair form. Ion pair fragmentation to the cation or anion as well as ion exchange and ion addition processes are observed by selected-ion flow tube mass spectrometry. Free energies of the reactions involving 1-ethyl-3-methylimidazolium bis-trifluoromethylsulfonylimide determined by ab initio quantum mechanical calculations indicate that ion exchange or ion addition are energetically more favorable than charge-transfer processes, whereas charge-transfer processes can be important in reactions involving 1-butyl-3-methylimidazolium dicyanamide