Effects of ion pairing

An important factor affecting redox potentials is also ion pairing, which is conventionally taken into account in terms of activity coefficients. For redox potentials of coordination compounds, the following equation is known [70]  

In electroanalysis, Eq. (23) forms the basis of highly sensitive techniques of potentiometric titration. The practical apphcations are presented by numerous potentiometric sensors, particularly biosensors [71-74]. The potential measurements in microheterogeneous media (microemulsions anionic, cationic and nonionic micelles) were worked out recently [75]. A separate field is the potentiometric studies of liquid/liquid junctions directed to the determination of ionic transport numbers. 

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Fig. 1. Effect of ion pairing on stereochemistry of propagation for alkyl vinyl ethers, where L is large substituent S, small substituent.

Guo, D.C., Mant, C.T., Hodges, R.S. (1987). Effects of ion-pairing reagents on the prediction of peptide retention in reversed-phase high-performance liquid chromatography. J. Chromatogr. 386, 205-222. 

Radon daughter ions and the ionization caused by the decay chains of radon and thoron in indoor air play important roles both from the contribution made by the daughter product positive ions to internal dose and from the effects of ion-pair production on the indoor atmospheric electrical parameters. 

Hi) Effect of ion-pair formation, and (/v) Effect of synergistic extraction... 

W. J. Vining, J. V. Caspar, and T. J. Meyer, Influence of environmental effects on excited state lifetimes. The effect of ion pairing on metal-to-ligand charge transfer excited states, J. Phys. Chem. 89, 1095-1099(1985). 

Finally, as an example of the effect of ion-pairing of surfactant counterions with co-moving ions, the reaction of methyl 4-nitrobenzenesulfonate with Br was accelerated when the concentration of Br in the Stern region was increased through the appropriate choice of cation. 

The composition of the solution should closely approximate the natural aqueous phase so that the effects of ion pairing and complexation are accounted for. 

The solution thus consists of different particles denoted as contact ion pairs, solvent-separated ion pairs and free ions. The fraction of the individual particles depends on the type of salt, type of solvent, polymerization system, temperature, and salt concentration. The catalytic effect of these particles may be very different as is evident in anionic polymerization of vinyl monomers. For instance, free polystyryl anion is 800times more reactive than its ion pair with the sodium counterion 60 . From this fact it follows that, although the portion of free ions is small in the reaction system, they may play an important role. On the other hand, anionic polymerization and copolymerization of heterocycles proceeds mostly via ion pairs. This is due to a strong localization of the negative charge on the chain-end heteroatom which strongly stabilizes the ion pair itself62. Ionic dissociation constants and ion contributions to the reaction kinetics are usually low. This means that for heterocycles the difference between the catalytic effect of ion pairs and free ions is much weaker than for the polymerization of unsaturated compounds. This is well documented by the copolymerization of anhydrides with epoxides where the substi-... 

The reactions of picryl fluoride with (2,3-dihydroxypropyl)-ammonium or -phosphonium compounds have been found120 to yield zwitterionic spiro-cr-adducts such as (31). Aromatic diazonium cations have been shown to add to the 9-position of cr-adducts of 9-nitroanthracene to yield neutral derivatives.121 A study has been reported of the effects of ion pairing and change of solvent on the kinetics of decomposition of some anionic cr-adducts.122... 

S. E. Landau, K. E. Groh, A. J. Lough and R. H. Morris, Large effects of ion pairing and protonic-hydridic bonding on the stereochemistry and basicity of crown-azacrown, and cryptand-222-potassium salts of anionic tetrahydride complexes of iridium(III). Inorg. Chem. 41, 2995-07 (2002). 

Only a few cases of effects of ion pairing upon the substrate are known, simply because such effects are not easy to demonstrate due... 

This article reviews the experimental evidence, accumulated in our laboratory, relating to different mechanisms involved in reactions of trityl and tropylium ions with reactive olefins and cyclic ethers and outlines the probable effect of ion pair equilibria on these reactions. 

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