Cation solvating ability

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

The development and the application of polymeric composite materials filled with nanosized rigid particles (essentially inorganic) has attracted both scientific and industrial interest. The development of new polymer electrolytes is needed for many kinds of electrochemical applications such as separators in high-energy density lithium batteries. Poly(oxyethylene) (POE)-based polymer electrolytes are the most commonly studied, due to their cationic solvation ability [188]. 

Fig. 12. Structural formulas of some compounds with specific cation-solvating abilities [136]...

In mixed solvent systems the difference in the solvating abilities of solvent molecules S and S2 causes a selective solvation of cations and anions [119,120],... 

Radical cations of the most popular spin traps PBN and DMPO have been generated by the methods of ionizing radiolysis and laser flash-photolysis in solid matrices (435-437). As a polar solvent with high solvating ability for... 

In solutions the energy of cation solvation decreases in the order Li + > Na+ > K+, so their ability for complexing with acetylene should change in favor of potassium to an even greater extent. With only semi-quantitative data available (yields of pyrroles), it is not possible to exactly establish the reason for the different catalytic activity of bases in this reaction. 

A solvent, in addition to permitting the ionic charges to separate and the electrolyte solution to conduct an electrical current, also solvates the discrete ions, firstly by ion-dipole or ion-induced dipole interactions and secondly by more direct interactions, such as hydrogen bonding to anions or electron pair donation to cations. The latter interactions, thus, depend on the Lewis acidity and basicity, respectively, of the solvents (Table 4.3). The redox properties of the ions at an electrode therefore depend on their being solvated, and the solvent effects on electrode potentials or polarographic half wave potentials, or similar quantities in voltammetry are manifested through the different solvation abilities of the solvents. 

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