Cationic equilibrium

It is believed that this greater interaction of 812BMG with + anions than with cations is due, not to the zwitterionic betaine, B , but to the cationic protonated betaine, B8, in equilibrium with it. Although the concentration of B8 at p8 = 5.8 is very small, it is felt that strong electrostatic interaction between it and an anion can displace the zwitterion-cation equilibrium sufficiently to cause an appreciable effect. 

This interesting effect is associated with the reversible leuco -triphenylmethyl cation equilibrium shown in Scheme 8 which also gives rise to an intensive colour change. 

An example of nonideal organic-phase behavior arises with di-2-ethylhexy phosphoric acid (DEHPA) in the extraction or metal cations. Equilibrium data of Troyer9 for extraction of copper in the presenes of nickel from sulfate solution into xylene solutions of DEHPA are shown in Fig. 8.3-10. Although the organic-phase copper concentration would be expected to rise in proportion to that in the aqueous phase,... 

The activities of Li2ZrCl6, Na2ZrCl6, and K2ZrCl0 in the systems MCl-MaZrClg were recalculated from available vapor pressure data (186). Previously reported calculations (342) for the sodium and potassium chloride systems are now known to be in error. The calculations indicate positive deviations from ideality that decrease with increasing size of the alkali metal cation. Equilibrium constants for the dissociation... 

FIGURE 15.6 (a, b) Typical curves for anion and cation equilibrium adsorption in the micropores of activated carbon electrodes, based on data from Ref. 12, expressed as moles of ions adsorbed per volume of micropores. Theoretical lines based on the modified-Donnan model. Note that the micropore charge is always higher than the salt adsorption. ( Salt adsorption relative to the situation of zero charge.)... 

We can translate the steric hindrance of the molecule by letting it to occupy several potential sites, which, in turn, after ionization gives a non-dissociable entity later on. For example, the molecule can be associated with a cation vacancy that cannot move separately and thus no longer takes part in cationic equilibriums of the solid. 

Ionic conductors arise whenever there are mobile ions present. In electrolyte solutions, such ions are nonually fonued by the dissolution of an ionic solid. Provided the dissolution leads to the complete separation of the ionic components to fonu essentially independent anions and cations, the electrolyte is tenued strong. By contrast, weak electrolytes, such as organic carboxylic acids, are present mainly in the undissociated fonu in solution, with the total ionic concentration orders of magnitude lower than the fonual concentration of the solute. Ionic conductivity will be treated in some detail below, but we initially concentrate on the equilibrium stmcture of liquids and ionic solutions. 

The hydration of more inert ions has been studied by O labelling mass spectrometry. 0-emiched water is used, and an equilibrium between the solvent and the hydration around the central ion is first attained, after which the cation is extracted rapidly and analysed. The method essentially reveals the number of oxygen atoms that exchange slowly on the timescale of the extraction, and has been used to establish the existence of the stable [1 10304] cluster in aqueous solution. 

Acetic acid and other carboxylic acids are protonated in superacids to form stable carboxonium ions at low temperatures. Cleavage to related acyl cations is observed (by NMR) upon raising the temperature of the solutions. In excess superacids a diprotonation equilibrium, indicated by theoretical calculations, can play a role in the ionization process. 

Protonation of formic acid similarly leads, after the formation at low temperature of the parent carboxonium ion, to the formyl cation. The persistent formyl cation was observed by high-pressure NMR only recently (Horvath and Gladysz). An equilibrium with diprotonated carbon monoxide causing rapid exchange can be involved, which also explains the observed high reactivity of carbon monoxide in supera-cidic media. Not only aromatic but also saturated hydrocarbons (such as isoalkanes and adamantanes) can be readily formylated. 

The two dimers of (CH3)2C=CH2 are formed by the mechanism shown m Figure 6 16 In step 1 protonation of the double bond generates a small amount of tert butyl cation m equilibrium with the alkene The carbocation is an electrophile and attacks a second molecule of 2 methylpropene m step 2 forming a new carbon-carbon bond and generating a carbocation This new carbocation loses a proton m step 3 to form a mixture of 2 4 4 tnmethyl 1 pentene and 2 4 4 tnmethyl 2 pentene... 

Ion-Exchange Equilibrium. Retention differences among cations with an anion exchanger, or among anions with a cation exchanger, are governed by the physical properties of the solvated ions. The stationary phase will show these preferences ... 

Potentiometric electrodes are divided into two classes metallic electrodes and membrane electrodes. The smaller of these classes are the metallic electrodes. Electrodes of the first kind respond to the concentration of their cation in solution thus the potential of an Ag wire is determined by the concentration of Ag+ in solution. When another species is present in solution and in equilibrium with the metal ion, then the electrode s potential will respond to the concentration of that ion. Eor example, an Ag wire in contact with a solution of Ck will respond to the concentration of Ck since the relative concentrations of Ag+ and Ck are fixed by the solubility product for AgCl. Such electrodes are called electrodes of the second kind. 

In pure and stoichiometric compounds, intrinsic defects are formed for energetic reasons. Intrinsic ionic conduction, or creation of thermal vacancies by Frenkel, ie, vacancy plus interstitial lattice defects, or by Schottky, cation and anion vacancies, mechanisms can be expressed in terms of an equilibrium constant and, therefore, as a free energy for the formation of defects, If the ion is to jump into a normally occupied lattice site, a term for... 

Trifluoromethylpteridine and its 7-methyl and 6,7-dimethyl derivatives (69JCS(C)l75l) are, as expected, even more subject to hydration. The first two are essentially completely hydrated across the 3,4-double bond at equilibrium in neutral solution and the last is partly hydrated. On dissolution of 4-trifluoromethylpteridine in aqueous acid the 5,6,7,8-dihy-drated cation is the main product initially, rearranging more slowly to the thermodynamically more stable 3,4-hydrate. 

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