Halide ions parameters

It is noteworthy that the best results could be obtained only with very pure ionic liquids and by use of an optimized reactor set-up. The contents of halide ions and water in the ionic liquid were found to be crucial parameters, since both impurities poisoned the cationic catalyst. Furthermore, the catalytic results proved to be highly dependent on all modifications influencing mass transfer of ethylene into the ionic catalyst layer. A 150 ml autoclave stirred from the top with a special stirrer... 

Such differences of the thermal IR emission spectra of compounds that consist of oxygen-containing ions and halide ions are related to the relationships between the compounds optical parameters. 

Ahrland et al. (1958) classified a number of Lewis acids as of (a) or (b) type based on the relative affinities for various ions of the ligand atoms. The sequence of stability of complexes is different for classes (a) and (b). With acceptor metal ions of class (a), the affinities of the halide ions lie in the sequence F > Cl > Br > I , whereas with class (b), the sequence is F < Cl" < Br < I . Pearson (1963, 1968) classified acids and bases as hard (class (a)), soft (class (b)) and borderline (Table 1.23). Class (a) acids prefer to link with hard bases, whereas class (b) acids prefer soft bases. Yamada and Tanaka (1975) proposed a softness parameter of metal ions, on the basis of the parameters En (electron donor constant) and H (basicity constant) given by Edwards (1954) (Table 1.24). The softness parameter a is given by a/ a - - P), where a and p are constants characteristic of metal ions. 

Among the potential impurities in ionic liquids water, halide ions and organic starting material are of great importance for transition metal chemistry while the colour of an ionic liquid is not a critical parameter in most applications. 

Picosecond absorption spectroscopy was employed to study the dynamics of contact ion pairs produced upon the photolysis of substituted diphenylmethyl acetates in the solvents acetonitrile, dimethyl sulfoxide, and 2,2,2-trifluoroethanol.66 A review appeared of the equation developed by Mayr and co-workers log k = s(N + E), where k is the rate constant at 20 °C, s and N are nucleophile-dependent parameters, and is an electrophilicity parameter 67 This equation, originally developed for benzhydrylium ions and n-nucleophiles, has now been employed for a large number of different types of electrophiles and nucleophiles. The E, N, and s parameters now available can be used to predict the rates of a large number of polar organic reactions. Rate constants for the reactions of benzhydrylium ions with halide ions were obtained... 

Joung, I. S., and Cheatham, T. E. Ill (2008). Determination of alkali and halide monovalent ion parameters for use in explicitly solvated biomolecular simulations. J. Phys. Chem. B 112, 9020-9041. 

Figure 1(a), (b), and (c) show the X-ray radial distribution functions (RDF) for the 10.6 m LiCl, 11.2 m LiBr, and 11.1 m Lil aqueous solutions, respectively, at the various temperatures. The first prominent peak observed at 3.1 - 3.6 A in the RDFs corresponds mainly to the halide-water interactions due to the halide hydration. The contribution of the water-water interactions within the primary hydration shell of Li also falls within this range. A characteristic feature of the RDFs with temperature is an appearance of a new peak centered at 4.3 A. The position of the peak does not depend on the halide ions the peak is gradually enhanced with lowering temperature. We have previously assigned this peak mainly to water-water interactions for the 11m aqueous LiCl solution. The quantitative analysis has been made by a least-squares fitting procedure, and the important structural parameter values finally obtained are summarized in Table 2. The evolution of the 4.3 A peak with lowering temperature is clearly seen in Fig. 

Figure 3.10. Estimation of difference in affinity (AAG) of the two anions Cl and Br for the cryptand SC24 [(a) structural formula (b) schematic of complex formed with halide ion] as the parameters for Cl are slowly mutated into those for Brin water (- - -) as well as in the complex —). Used with permission (138).

Experiments carried out on monocrystalline Au(lll) and Au(lOO) electrodes in the absence of specific adsorption did not show any fre-quency dispersion. Dispersion was observed, however, in the presence of specific adsorption of halide ions. It was attributed to slow adsorption and diffusion of these ions and phase transitions (reconstructions). In their analysis these authors expressed the electrode impedance as = R, + (jco iJ- where is a complex electrode capacitance. In the case of a simple CPE circuit, this parameter is = T(Jcaif. However, an analysis of the ac impedance spectra in the presence of specific adsorption revealed that the complex plane capacitance plots (C t vs. Cjnt) show the formation of deformed semicircles. Consequently, Pajkossy et al. proposed the electrical equivalent model shown in Fig. 29, in which instead of the CPE there is a double-layer capacitance in parallel with a series connection of the adsorption resistance and capacitance, / ad and Cad, and the semi-infinite Warburg impedance coimected with the diffusion of the adsorbing species. A comparison of the measured and calculated capacitances (using the model in Fig. 29) for Au(lll) in 0.1 M HCIO4 in ths presence of 0.15 mM NaBr is shown in Fig. 30. 

The N parameters indicate the unusual order Br > I > Cl for the abilities of the halogens to depart as halide ions from the trihalocarbanions. An investigation of the hydrolysis of bromochloroiodomethane in the presence of sodium iodide has shown that chloroiodocarbene is in fact the major intermediate. ... 

Expressions for the force constant, i.r. absorption frequency, Debye temperature, cohesive energy, and atomization energy of alkali-metal halide crystals have been obtained. Gaussian and modified Gaussian interatomic functions were used as a basis the potential parameters were evaluated, using molecular force constants and interatomic distances. A linear dependence between spectroscopically determined values of crystal ionicity and crystal parameters (e.g. interatomic distances, atomic vibrations) has been observed. Such a correlation permits quantitative prediction of coefficients of thermal expansion and amplitude of thermal vibrations of the atoms. The temperature dependence (295—773 K) of the atomic vibrations for NaF, NaCl, KCl, and KBr has been determined, and molecular dynamics calculations have been performed on Lil and NaCl. Empirical values for free ion polarizabilities of alkali-metal, alkaline-earth-metal, and halide ions have been obtained from static crystal polarizabilities the results for the cations are in agreement with recent experimental and theoretical work. 

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