Ion pair association

One can write acid-base equilibrium constants for the species in the inner compact layer and ion pair association constants for the outer compact layer. In these constants, the concentration or activity of an ion is related to that in the bulk by a term e p(-erp/kT), where yp is the potential appropriate to the layer [25]. The charge density in both layers is given by the algebraic sum of the ions present per unit area, which is related to the number of ions removed from solution by, for example, a pH titration. If the capacity of the layers can be estimated, one has a relationship between the charge density and potential and thence to the experimentally measurable zeta potential [26]. 

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],... 

The conductivity functions of such electrolytes can be evaluated at the level of limiting laws with the help of Eq. (18), permitting the determination of the tripleion-constant KT and the ion-pair association constant KA. 

In contrast to bilateral triple-ion formation, unilateral triple-ion formation may also occur in solvents of high permittivity, when ion-pair association is increased by noncoulombic specific ion-ion interactions in solvents of low basicity such as PC or AN. Exclusive formation of anionic tripleions [A-C+A-] ", is observed in these solvents when large organic molecular anions A interact with small cations such as Li + or H+. For example, in contrast to lithium acetate in DMSO [97], where ion association is moderate, ion association as well as unilateral triple-ion formation is observed in the solvent PC [105] due to the much lower basicity of this solvent, (see Table 2)... 

Table 5 contains a selection of ion-pair association constants, triple ion formation constants, and limiting conductivities for various electrolytes which have been studied in connection with the optimization of battery electrolytes. It shows... 

Cationic surfactants show a high affinity for negatively charged surfaces making them suitable for industrial applications and as components for consumer products where they are used as disinfectants, foam depressants, and first and foremost as textile softeners [23], Due to the possible formation of ion-pair associates they are usually not formulated together with anionic surfactants. 

Ion pair association constants measured by conductance have not often been verified by independent techniques, but where comparisons have been made agreement appears satisfactory. For example, a value of 70.2 0.5 was obtained for the association constant of silver nitrate in acetonitrile by conductance l0), and a value of 74 5 by potentiometric measurements, 44) of the cell... 

These new methods for determining the partition coefficients of ionized species are still e3q>erimenta1, but they are presented in a spirit that they may stimulate thinking and further refinement. Single-phase titrations with HCl in octanol have only recently been run. A possible concentration dependency of pKa in the single-phase titrations has been suggested by a referee and will be looked for. Further refinement of the two-phase titrations may incorporate ion-pair association constants. 

The situation is similar qualitatively but differs quantitatively for isoprene and 1,3-buta-diene. The dependence of Rp on initiator varies from g- to -order depending on the specific reaction system. The reaction orders for all monomers are affected hy the relative as well as absolute concentrations of initiator and monomer. Thus the dependence of Rp on initiator for the n-butyllithium polymerization of isoprene in benzene at 30°C is -order at initiator concentrations above 10-4 M but -order at initiator concentrations below 10 4 M [Van Beylen et al., 1988]. Higher initiator concentrations yield higher degrees of aggregation and lower kinetic orders. The excess of monomer over initiator is also important. Higher kinetic orders are often observed as the monomer initiator ratio increases, apparently as a result of breakup of initiator and propagating ion-pair associations by monomer. 

In the case of sulfate and dihydrogen phosphate where the ion pair association constants have been clearly identified, the anation rates are known for the 1 1 outer sphere complex. These rate values vary somewhat, and this perhaps indicates participation of the entering group. But there may be another way to interpret what is going on. These two rates of anion entry are smaller than the rate of water exchange of the aquopentammine complex. In fact, the univalent anion enters the complex from the outer sphere at approximately one-eighth of the rate of water exchange, and the divalent anion enters the complex from the outer sphere about twice as fast. 

Strathmann, T. J., and C. T. Jafvert, Ion-pair association of substituted phenolates with K+ in octanol , Environ. Toxicol. Chem., 17, 369-376 (1998). 

Accordingly, we might expect triphenylmethyl (or trityl) halides, (C6H5)3C—X, to be even more reactive. In fact, the C-X bonds of such compounds are extremely labile. In liquid sulfur dioxide, triarylmethyl halides ionize reversibly, although the equilibria are complicated by ion-pair association ... 

We focus on the conductance data. In systems of the type considered here, the conductance is primarily determined by the degree of ion pair association a. However, at higher ion densities, substantial mobility effects come into play. In the absence of sufficiently accurate conductance theories for the region of interest, a reliable measure for estimating a. is the conductance-viscosity product Arj which is often denoted as the Walden product. Figure 7 shows isotherms for the Walden product at T Si Tc for Bu4NPic + 1-tridecanol [72] and Bu4NPic + 1-chloroheptane [137] as a function of the... 

The proper treatment of ionic fluids at low T by appropriate pairing theories is a long-standing concern in standard ionic solution theory which, in the light of theories for ionic criticality, has received considerable new impetus. Pairing theories combine statistical-mechanical theory with a chemical model of ion pair association. The statistical-mechanical treatment is restricted to terms of the Mayer/-functions which are linear in / , while the higher terms are taken care by the mass action law... 

Early ESR studies demonstrated that the hyperfine coupling constant (ac 13) for 13C(car-bonyl)-substituted fluorenone radical anion is counterion-dependent. For the free ion, ac 13 = 2.75 Gauss. In contrast, when the counterion is Li+, ac 13 = 6.2 Gauss23. Consider Scheme 4 For the free ion, canonical structure 1 and 2 are contributors to the resonance hybrid. For the >C=0 / Li+ ion pair, association of Li+ with oxygen increases the relative contribution of canonical structure 1 to the resonance hybrid, resulting in greater spin density at carbon. The fact that spin (and charge density) varies as a function of counterion (and presumably solvent) will certainly affect the reactivity of the radical ion. However, very few quantitative studies exist which directly address this point. 

The quaternary ammonium cation, tricaprylylmethylammonium, is a well known ion-pairing extracting agent and was used to obtain the ion-pair association complex with 5,5-diphenylhydantoinate anion. The ion-pair complex was embedded in a PVC matrix, containing NPOE as plasticizer. The membrane composition was 7.7% (w/w) electroactive material, 61.5% (w/w) NPOE and 30.8% (w/w) PVC. 

There is one rather nasty twist in the ion pair evaluation where a negative value for free carbonate ion concentration results, because the initial value which must be used for the carbonate ion activity coefficient is much larger than it is under the new conditions. This demands some maneuvers with both the calcite solubility constant and the calcium carbonate ion pair association constant. These will not be gone into here. 

Mayer [22], the above correlations indeed work well and are quite useful for predicting values such as the free energy of salt solutions and complex formation in various solvents. Another typical example of the importance of the use of DN and AN as solvent parameters, instead of properties such as the dielectric constant, would be ion pair association constants in isodielectric solvents. For instance, as shown by Mayer [15], association constants of various perchlorates isocyanates, and halides (alkali metal, ammonium, and tetraalkyl ammonium cations) are very different in isodielectric solvents such as nitromethane (DN = 2.7), acetonitrile (DN = 14.1), and DMF (DN = 26.6), whose dielectric constant is around 26 at room temperature. 

As reported by Venkatassety [34], evaluation of the conductivity of dipolar aprotic solutions must take into account, in addition to ion pair association and triple ion formation, the possibility of strong ion-solvent interactions and the pronounced effect of solvent viscosity on the conductivity. A typical example is PC solution of Li salts, where the A0 values calculated (based on conductivity measurements) were found to be very low in spite of the high polarity of this solvent and the expected high degree of dissociation of the electrolytes, due to the high viscosity of this solvent. 

In lithium alkyl-initiated polymerizations only chain initiation and propagation steps need be considered in hydrocarbon solvents. Both reactions are strongly influenced by extensive association of all lithium compounds. The reactive species in chain propagation is the small amount of dissociated material which probably exists as an ion pair. Association phenomena disappear on adding small amounts of polar additives, and the aggregates are replaced by solvated ion pairs. In polar solvents of relatively high dielectric constant (e.g. tetrahydrofuran), some dissociation of the ion pairs to free ions occurs, and both species contribute to the propagation step. The polymerizations are often complicated in tetrahydrofuran by two side reactions, namely carbanion isomerization and reaction with the solvent. 

Reductive properties of excited state organic anions are discussed, starting from the preliminary presentation of other related properties spectral characteristics, ion pair associations and photoejection ability. 

The electrical conductivities of electrolyte solutions and the ion-pair association constant are both very sensitive to ion solvation and permit the calculation of solvation constants. 

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