No abstract

The specific ionic conductivity, dynamic viscosity, and electrochemical stability of several imidazolium salts are reported as neationic liquids and their solutions in several organic solvents. The temperature dependence of conductivity and viscosity are analyzed for 1‐ethyl‐3‐methylimidazolium false(EMI+false) and 1,2‐dimethyl‐3‐n‐propylimidazolium false(DMPI+false) salts, and the influence of theanions bis(trifluoromethylsulfonyl)imide false(Im−false) , bis(perfluoroethylsulfonyl)imide false(Beti−false) , hexafluoroarsenate false(AsF6−false) , hexafluorophosphate false(PF6−false) , and tetrafluoroborate false(BF4−false) on these properties are discussed. These imidazolium salts make possible electrolytes with high concentration (>3 M), high room temperature conductivity (up to 60 mS/cm), and a wide window of stability false(>4Vnormalat 20 μA/cm2false) . Differential scanning calorimetric results confirm a large glass phase for the ionic liquids, with substantial (>80°C) supercooling. Thermal gravimetric results indicate the imidazolium salts with Im− and Beti− anions to be thermally more stable than the lithium salt analogs. The Vogel‐Tammann‐Fulcher interpretation accurately describes the conductivity temperature dependence. © 1999 The Electrochemical Society. All rights reserved.

Measurements were made for the rate constant of OH + CO + He at 293 K, and OD + CO + M (M = He, Ar, N2, air, SF6) at 253−343 K. Results were also obtained for OH + CO in a shock tube at 1400−2600 K using OH and CO absorption. A two-channel RRKM model of these and other representative results was constructed, with five adjustable parameters. A systematic optimization method was then employed to produce the best fit of the data and provide predictive k(T,P,D/H) expressions for other conditions.

Electrolytes based on 1-ethyl-3-methylimidazolium cation (EMI + ) and either the hexafluorophosphate (EMIPF 6 ) or tetrafluorborate (EMIBF 4 ) anion in organic alkyl carbonate solvents have been evaluated for use in electrochemical capacitors. The conductivity, capacitance, limiting oxidation and reduction potentials, and thermal stability were assessed. High conductivity and capacitance values were found regardless of whether cyclic (high viscosity/high dielectric constant) or acyclic (low viscosity/low dielectric constant) alkyl carbonates were used. The best correlation with conductivity for the EMIPF, salt was found to be the molecular weight (K-1/Mw) and to a lesser degree the viscosity (Kc1/i) of the solvent. The high specific capacitance (130 F/g) and excellent stability (>3.5 V, >130°C) make these electrolytes well suited for use in electrochemical double-layer capacitors.

In-plane 4n + 2 aromaticity in hydrocarbons containing radial p orbitals is predicted in suitably constituted uncharged polyolefinic systems. Several criteria were employed to investigate aromaticity in [n] peristylapolyenes ( = 3-5), p-[41 2.58]hexadecahedrapolyenes, dodecahedrapolyenes, and tetraquinapolyenes by using Allinger's MMP2 program. In the most favorable cases, after correction for strain effects, modest but significant w stabilization energies are indicated. MNDO semiempirical calculations also indicate a cyclic conjugated dodecahedrapentaene to be aromatic. In addition, the possibility of trishomoaromaticity in known and several previously unknown trienes was investigated, but these are no more than slightly favorable. Geometrical restrictions imposed by the framework in such cases prevent adequate overlap of the orbitals.