K Ion Pairs

The addition of mercury in reaction mixtures of nitroarylsulfenates with C8H8K2 in THF did not change the reaction results. Disintegration of the XSC6H4NO2 K+ ion pairs (controlled via ESR) does not affect the reaction results either. 

Mohapatra, P.K. Manchanda, V.K. Ion-pair extraction of uranyl ion from aqueous medium using crown ethers, TalantaAl (1998) 1271-1278. 

FIG. 1.12. The structure of K HgCU. HjO viewed along the direction of the infinite chains. The K ions (pairs of overlapping circles) and HjO molecules (large circles) lie, at various... 

In subsequent work, the effect of the sizes of the cation and the associated [(M+)(SiVWnO405-)]4- (M+=Fi+, Na+, K+) ion pairs—the same ion pairs in Equation (9) above—on both the rate of oxidation of an organic substrate and the energy of electron transfer to these ion pairs was addressed.93 The organic substrate used was a diphenol (DPH2) because it is oxidized cleanly by these ion pairs to the corresponding diphenoquinone (DPQ) (Equation (12))... 

Weinstock, I. A. Grigoriev, V. A. Cheng, D. Hill, C. L. Role of Alkali-Metal Cation Size in Electron Transfer to Solvent-Separated 1 l[(M+)(POM)] (M+ = Li+Na+K+) Ion Pairs. In Polyoxometalate Chemistry for Nano-composite Design Yamase, T., Pope, M. T., Eds. Kluwer Academic/Plenum Publishers New York, 2002 103-129. 

ROLE OF ALKALI-METAL CATION SIZE IN ELECTRON TRANSFER TO SOLVENT-SEPARATED 1 1 ((M )(P0M)J (M = Li/ Na/ K ) ION PAIRS... 

We herein summarize data that address issues (1) to (3) and provide new information regarding the physicochemical role of alkali-metal cation (M ) size in electron-transfer to 1 1 [(M )(POM)] (M = Li/ Na, K" ) ion pairs. To achieve this, a-SiV Wn04o (l. Fig. 1), was used as a stoichiometric le acceptor in the 2e oxidation of a phenolic electron donor, 3,3, 5,5 -tetra-tert-butylbiphenyl-4,4 -diol (BPH ) to... 

At this time we do not attempt to assign all of the P NMR peaks observed at low water concentration. Most likely the peaks that disappear first as water is added (at 175 and 440 ppm) originate from the PWnCo ion with the empty sixth coordination site on cobalt. One of these species could have K ion paired to the heteropoly anion. We continue to investigate this phenomenon for PWnCo and other heteropoly mngstates. 

Sekiguchi S, Kobori Y, Akiyama K and Tero-Kubota S 1998 Marcus free energy dependence of the sign of exchange interactions in radical ion pairs generated by photoinduced electron transfer reactions J. Am. Chem. Soc. 120 1325-6... 

The preparation of an ion-selective electrode for salicylate is described. The electrode incorporates an ion-pair of crystal violet and salicylate in a PVC matrix as the ion-selective membrane. Its use for the determination of acetylsalicylic acid in aspirin tablets is described. A similar experiment is described by Creager, S. E. Lawrence, K. D. Tibbets, C. R. in An Easily Constructed Salicylate-Ion-Selective Electrode for Use in the Instructional Laboratory, /. Chem. Educ. 1995, 72, 274-276. 

The general formula for the initiator species can be written H B, where the degree of separation or ion pairing depends on the polarity of the medium and the possibility of specific solvation interactions. If we represent the equilibrium constant for the reactions in (6.DD) and (6.EE) by K, the initiator concentration can be written as... 

Ionic polymers may exist as undissociated, unsolvated ion pairs undissociated ion pairs solvated to some extent solvated ions dissociated to some extent or some combination of these. The propagation rate constant kp and the dissociation equilibrium constant K of the lithium salt of anionic... 

If it is assumed that ionization would result in complete randomization of the 0 label in the caihoxylate ion, is a measure of the rate of ionization with ion-pair return, and is a measure of the extent of racemization associated with ionization. The fact that the rate of isotope exchange exceeds that of racemization indicates that ion-pair collapse occurs with predominant retention of configuration. When a nucleophile is added to the system (0.14 Af NaN3), k y, is found to be imchanged, but no racemization of reactant is observed. Instead, the intermediate that would return with racemization is captured by azide ion and converted to substitution product with inversion of configuration. This must mean that the intimate ion pair returns to reactant more rapidly than it is captured by azide ion, whereas the solvent-separated ion pair is captured by azide ion faster than it returns to racemic reactant. 

The order of enolate reactivity also depends on the metal cation which is present. The general order is BrMg < Li < Na < K. This order, too, is in the order of greater dissociation of the enolate-cation ion pairs and ion aggregates. Carbon-13 chemical shift data provide an indication of electron density at the nucleophilic caibon in enolates. These shifts have been found to be both cation-dependent and solvent-dependent. Apparent electron density increases in the order > Na > Li and THF/HMPA > DME > THF >ether. There is a good correlation with observed reactivity under the corresponding conditions. 

In the polar pores, the diffusion coefficient of all ions is strongly reduced relative to the bulk values. No counterion dependence is observed for the SDC of CP. A more detailed analysis shows that the ion SDC depends on the ion s relative position in the pore [174]. In the case of the K ion, this dependence is particularly strong. K ions forming contact pairs with the surface charges are almost completely immobilized on the time scale of the simulations. The few remaining ions in the center of the pore are almost unaffected by the (screened) surface charges. The fact that most of the K ions form contact pairs substantially reduces the average value of the normalized K SDC to 0.2. The behavior of CP is similar to that of K. The SDC of sodium ions, which... 

Figure 4.11 Molecular structures of typical crown-ether complexes with alkali metal cations (a) sodium-water-benzo-I5-crown-5 showing pentagonal-pyramidal coordination of Na by 6 oxygen atoms (b) 18-crown-6-potassium-ethyl acetoacetate enolate showing unsymmelrical coordination of K by 8 oxygen atoms and (c) the RbNCS ion pair coordinated by dibenzo-I8-crown-6 to give seven-fold coordination about Rb.

K. Yamashita, M. Motohaslii and T. Yashiki, Sensitive high-performance liquid cliro-matographic determination of propranolol in human plasma with ultraviolet detection using column switcliing combined with ion-pair cliromatography , J. Chromatogr. 527 196-200(1990). 

Suppose that we arbitrarily set the partial molal entropy of the K+ ion equal to zero. This means that we assign to the Cl- ion the whole of the partial molal entropy of the ion pair (K+ + Cl-) that is to say, we assign to the Cl- ion, not only the unitary term for the Cl- ion, but also the cratic term for both ions, and also the unitary term for the potassium ion. 

The conclusions are evidently relevant to the amount of entropy lost by ions in methanol solution—see Table 29. If, however, the expression (170) is used for an atomic ion, we know that it is applicable only for values of R that are large compared with the ionic radius—that is to say, it will give quantitative results only when applied to the solvent dipoles in the outer parts of the co-sphere. The extent to which it applies also to the dipoles in the inner parts of the co-sphere must depend on the degree to which the behavior of these molecules simulates that of the more distant molecules. This can be determined only by experiment. In Table 29 we have seen that for the ion pair (K+ + Br ) and for the ion pair (K+ + Cl-) in methanol the unitary part of ASa amounts to a loss of 26.8 e.u. and 30.5 e.u., respectively, in contrast to the values for the same ions in aqueous solution, where the loss of entropy in the outer parts of the co-sphere is more than counterbalanced by a gain in entropy that has been attributed to the disorder produced by the ionic field. 

The saturated solution of potassium iodate in water at 25°C has a molality equal to 0.43. Taking the activity coefficient y in this saturated solution to be 0.52, find the conventional free energy of solution at 25°C, and calculate in electron-volts per ion pair the value of L for the removal of tho ions K+ and (IOs) into water at 25°C. 

As seen from Tables 23 and 21 the ion pair (K+ + Cl") increases the viscosity of methanol but diminishes that of water. We recall that the values for the entropy of solution in Table 29 show a parallel trend in the galvanic cells of Sec. 112 placed back to back, this difference in ionic entropy between aqueous and methanol solutions would alone be sufficient to give rise to an e.m.f. We must ask whether this e.m.f. would be in the same direction, or in the direction opposite to the e.m.f. that would result from a use of (199). 

Ion-pair association constants K A determined with the set of conductivity equations (7)—(15) agree with those obtained from Eq. (18) and (19) [100]. Salomon and Uchiyama have shown that it is also possible to extend the directly Fuoss-Hsia equation to include triple-ion formation [104],... 

Figure 5. (a) The ( A, SO,) anion symmetric streching mode of polypropylene glycol)- LiCF,SO, for 0 M ratios of 2000 1 and 6 1. Solid symbols represent experimental data after subtraction of the spectrum corre-ponding to the pure polymer. Solid curves represent a three-component fit. Broken curves represent the individual fitted components, (b) Relative Raman intensities of the fitted profiles for the ( Aj, SO,) anion mode for this system, plotted against square root of the salt concentration, solvated ions ion pairs , triple ions, (c) The molar conductivity of the same system at 293 K. Adapted from A. Ferry, P. Jacobsson, L. M. Torell, Electrnchim. Acta 1995, 40, 2369 and F. M. Gray, Solid State Ionics 1990, 40/41, 637. 

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