Ion-pairing effects

Ion pairing effects on transition metal carbonyl anions. M. Y. Darensbourg, Prog. Inorg. Chem., 1985,33,221(138). 

Swinehart" believes that specific ion-pairing effects are important with both Na and K and that the rate law should be written... 

However, as stated above, the partition coefficients measured by the shake-flask method or by potenhometric titration can be influenced by the potenhal difference between the two phases, and are therefore apparent values which depend on the experimental condihons (phase volume ratio, nature and concentrahons of all ions in the solutions). In particular, it has been shown that the difference between the apparent and the standard log Pi depends on the phase volume raho and that this relationship itself depends on the lipophilicity of the ion [80]. In theory, the most relevant case for in vivo extrapolation is when V /V 1 as it corresponds to the phase ratio encountered by a drug as it distributes within the body. The measurement of apparent log Pi values does not allow to differentiate between ion-pairing effect and partihoning of the ions due to the Galvani potential difference, and it has been shown that the apparent lipophilicity of a number of quaternary ion drugs is not due to ion-pair partitioning as inihally thought [80]. 

Ionic dissociation of carbon-carbon a-bonds in hydrocarbons and the formation of authentic hydrocarbon salts, 30, 173 Ionization potentials, 4, 31 Ion-pairing effects in carbanion reactions, 15, 153 Ions, organic, charge density-NMR chemical shift correlations, 11,125 Isomerization, permutational, of pentavalent phosphorus compounds, 9, 25 Isotope effects, hydrogen, in aromatic substitution reactions, 2,163... 

Darensbourg, Marcetta York, Ion Pairing Effects on Metal Carbonyl Anions... 33 221... 

Although the theory of solutions has been widely used in formulating problems of defects in solids the problems encountered differ in certain respects. The most obvious point is that defects are restricted to discrete lattice sites, whereas the ions in a solution can occupy any position in the fluid. Sometimes no allowance is made for this fact. For example, it has not been demonstrated that at very low concentrations, in the absence of ion-pair effects, the activity coefficients are identical with those of the Debye-Hiickel theory. It can be plausibly argued51 that at sufficiently low concentrations the effect of discreteness is likely to be negligible, but clearly in developing a theory for any but the lowest concentrations the effect should be investigated. A second point... 

A number of differently sized crown ethers were synthesized and the shift of the first reduction potential was found for each compound in the presence of excess alkali metal tosylate. The shifts were all between 60 and 70 mV for compound [50] but the larger crowns displayed larger shifts (Table 10). In contrast to the expected order of the magnitudes of the shifts from ion pairing effects alone, K+ with compound [51] yields the largest potential shift followed by Rb+>Na+>Cs+>Li+. 

The independence of CH- carbon acidities from the solvent can be attributed to the fact that only highly delocalized carbanions have been considered. When aggregation or specific solvent ion-pairing effects are operative, deviations from this behaviour are expected. 

DR. RAMESH PATEL (Clarkson College) Couldn t one pick certain systems in which the ion pairing effect would be very large One would then be able to make some comments about the influence of volume changes on ion pair formation for rapidly exchanging systems. 

Ion-pairing effects may considerably influence disproportionation mechanisms that involve homogeneous redox reactions of anions to their respective dianionic and neutral species (Eq. 4) [52, 53],... 

It should be noted that ion interaction coefficients tabulated in Tables 6.3-6.5 may also involve ion pairing effects, as described in section 6.3. In direct comparisons of ion interaction coefficients, or when estimates are made by analogy, this aspect must be taken into account. 

Aquation rate constants [Co(NH,), X]", 34 165-166 ion pairing effects, 34 173 metal-assisted reactions, 34 168-169 pentaamminecobalt(III) complexes, 34 149 pentaamminemetal(III) complexes, 34 152-153... 

As noted in Section 4.2.1, the gas phase has proven to be a useful medium for probing the physical properties of carbanions, specifically, their basicity. In addition, the gas phase allows chemists to study organic reaction mechanisms in the absence of solvation and ion-pairing effects. This environment provides valuable data on the intrinsic, or baseline, reactivity of these systems and gives useful clues as to the roles that solvent and counterions play in the mechanisms. Although a variety of carbanion reactions have been explored in the gas phase, two will be considered here (1) Sn2 substitutions and (2) nucleophilic acyl substitutions. Both of these reactions highlight some of the characteristic features of gas-phase carbanion chemistry. 

Schulz, P.S., Muller, N., Bosmann, A. and Wasserscheid, P. (2007) Effective chirality transfer in ionic liquids through ion-pairing effects. Angew. Chem., Int. Ed., 46 (8), 1293-1295. 

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