Solvation or association

This implies that species i does not solvate or associate significantly. Otherwise, we set s equal to the minimum of one of the following for all j. ... 

Equations [1] and [2] describe the interaction of enantiomeric solutes A and A with chiral solvating agent S. Solvates (or association complexes) are formed that are diastereomeric and thus can, in principle, have different properties. Relevant differences are those in... 

Some recent work from this laboratory describes some experiments which have the potential of extracting gas phase data from studies in polar solvents 8, 12,13). Only when the solvent is properly selected for the particular system to be studied can one hope to approach data relatively free of solvation or association energies. For many systems, the solubility limitations clearly make quantitative measurement impossible at our present level of understanding. 

Unlike superelectrophiles generated in the condensed phase, the gas phase species are not stabilized by solvation or association to counter ions. The stabilities of multiply charged small ions are dependent on their tendencies to dissociate into fragments in the gas phase.39 For diatomic systems, there are two possible routes of dissociation to atomic fragments the cleavage to a pair of monocations (eq 41) or cleavage to a dication and neutral species (eq 42). 

Then the chemical contribution can be computed from the estimated true mole fractions. With the assumption that the mixture is ideal, chemical activities simply equal the true mole fractions of monomeric species, and Prigogine and Defay [60] have shown that, regardless of the solvation or association reactions that may occur, in an ideal true mixture with gpf = 0,... 

The role of crown ethers and their analogues as catalysts, co-catalysts, and substrates in reactions involving ions and ion pairs has been reviewed in Polish. States of solvation or association affect the reactivity of ionic reagents in spectacular ways. A series on mechanoactivated halogen-substitution reactions of alkyl halides has continued in a study of halogen substitution in ethyl bromide on the surface of mechanically... 

Naturally, the ability of a molecule to solvate or associate is intimately linked to its electronic structure. Hydrogen bonding can lead to either of these behaviors. An example of solvation is given by a mixture of chloroform and acetone. Hydrogen bonding causes the unlike molecules to form a complex ... 

D. The next card supplies the solvation and association parameters, and the third parameter for either the UNIQUAC, NRTL, or Wilson equation, if this parameter is not being fitted. 

Because the key operation in studying solvent effects on rates is to vary the solvent, evidently the nature of the solvation shell will vary as the solvent is changed. A distinction is often made between general and specific solvent effects, general effects being associated (by hypothesis) with some appropriate physical property such as dielectric constant, and specific effects with particular solute-solvent interactions in the solvation shell. In this context the idea of preferential solvation (or selective solvation) is often invoked. If a reaction is studied in a mixed solvent. 

For attempts in the literature to rationalize the maximum, with reference to solvation, ion association, or viscosity of the electrolyte, see Ref. [15]. 

Bu4NBr in AN/PC in the temperature range 75 °C>6>- 35°C a linear correlation /rmax 41) is found [209], independent of temperature and solvent composition. The use of high-permittivity solvents belonging to the same class suppresses the effects due to strong selective solvation or changing association. 

Carbocations are intermediates in several kinds of reactions. The more stable ones have been prepared in solution and in some cases even as solid salts, and X-ray crystallographic structures have been obtained in some cases. An isolable dioxa-stabilized pentadienylium ion was isolated and its structure was determined by h, C NMR, mass spectrometry (MS), and IR. A P-fluoro substituted 4-methoxy-phenethyl cation has been observed directly by laser flash photolysis. In solution, the carbocation may be free (this is more likely in polar solvents, in which it is solvated) or it may exist as an ion pair, which means that it is closely associated with a negative ion, called a counterion or gegenion. Ion pairs are more likely in nonpolar solvents. 

All of this suggests that the ion association explanation may be applied here to an essentially bimolecular (or associative) phenomenon. Considering the difference between hydroxide and any other reagent in water, apart from its basicity, one concludes that its mobility must play an important part. Whereas all the other reagents must be in a suitable position within the solvation shell before they can enter the complex, the hydroxide ion, by means of a Grotthus chain proton transfer, can be transmitted to any position where it is needed while the complex becomes activated. It can therefore be looked upon as an unsaturatable ion aggregate with hydroxide fully delocalized about the complex. Consequently, we do not observe any departure from the first-order dependence upon hydroxide concentration. This contribution to the reactivity will appear in the activation entropy rather than in the enthalpy term. 

As we shall see, the solution conductivity depends on the ion concentration and the characteristic mobility of the ions present. Therefore, conductivity measurements of simple, one-solute solutions can be interpreted to indicate the concentration of ions (as in the determination of solubility or the degree of dissociation) or the mobility of ions (as in the investigations of the degree of solvation, complexation, or association of ions). In multiple-solute solutions, the contribution of a single ionic solute to the total solution conductivity cannot be determined by conductance measurements alone. This lack of specificity or selectivity of the conductance parameter combined with the degree of tedium usually associated with electrolytic conductivity measurements has, in the past, discouraged the development of conductometry as a widespread electroanalyti-cal technique. Today, there is a substantial reawakening of interest in the practical applications of conductometry. Recent electronic developments have resulted in automated precision conductometric instrumentation and applications... 

In an apparently homogeneous solution, macromonomers, possibly together with the resulting graft copolymers, may lead to some structure formation such as micelle or looser association, which may in turn change the apparent reactivities due to some specific solvation or partition of the monomers around the active sites. Such a bootstrap effect [52] maybe responsible for some complicated dependency of the apparent reactivities on the monomer concentration and composition in radical copolymerization of 29 with n-butyl acrylate [53]. 

The addition of LiCl to the ionic liquid was found to have only a small effect upon the conductivity of the liquid, but it did affect the speciation [121], producing more of the [CrCLp2H20]. It was anticipated that the small Li+ ion would have a high mobility in the liquid but the conductivity is less than expected, suggesting that the ion must be strongly solvated or highly associated with the anion. 

One of the drawbacks of pure CO2 as supercritical solvent is the low solubility of polar compounds which is attributed to lack of a strong permanent dipole moment in CO2. In order to improve solvation and extraction power, a highly polar or associative liquid is added to SC-CO2 in small quantities as co-solvent. Ethanol is the co-solvent of choice for a number of reasons, including its superior mixibility (compared to water, for instance) with CO2 and its wide acceptance in pharmaceutical and food-related supercritical extractions. 

Dissociation — is the separation or splitting of a chemical compound (complexes, molecules, or salts) into two or more -> ions by dissolution and -> solvation, or by any other means, the breaking into smaller molecules, or radicals. In case of solvation, this results in an ioni-cally conducting -> electrolyte solution. D. usually occurs in a reversible manner. The opposite process is association or recombination. Assuming a reversible dissociation reaction in a chemical -> equilibrium of the form XY X + Y, the ratio of dissociation is quantified by the dissociation constant JCn, i.e JCn = where a denotes the activity of the species. The dissociation constants are frequently quoted as values of pAT = - log K. In mass spectrometry, the term is used in the meaning of a fragmentation, i.e., a decomposition of an ion into another ion of lower mass and one or more neutral species. 

From the foregoing considerations it is apparent that thermodynamic properties of compounds such as ionization constants or solubilities do not only depend on heterolytic dissociation energies but may be strongly influenced by free energies of solvation or free-energy contributions associated with changes in the state of aggregation. 

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