Solvation phenomena

Thus, the net influence of increased polarity on the rate (instants is, in this case as well as in polymerization of THF, eventually not attributable to the solvation phenomenon itself but to the stronger electrical microfields formed by more easily induced dipoles in more polar (and more polarizable) solvent molecules (e.g. CH3NO2 vs. 004). In this way, the energy of the ground state decreases and AGp becomes larger in more polar solvents, decreasing eventually the corre nding rate constants. 

When a solute is dissolved in a pure hydrogen-bond donor solvent, such as water or alcohol, all acceptor sites are involved in the solvation phenomenon. For example, the partition of phenols between water and organic phases now depends both on the oxygen and on the tt hydrogen-bond basicities, because of the excess of water molecules. From sets of water-solvent partition coefficients, Abraham has constructed a scale of effective or summation hydrogen-bond basicity, for about 350 solutes, of which... 

In addition to the microsolvation, the effect of solvation on the reaction has also been modeled by Re and Morokuma [111]. They demonstrated the significance of molecular solvation using the two-layered ONIOM method. The Sn2 pathway between CH3CI and OH ion in microsolvated clusters with one or two water molecules has been studied. This work highlighted the role of solvent in the chemical reaction and also the power of ONIOM model to predict complex systems. All these studies have undoubtedly brought out the significance of H-bonding in solute-solvent interaction, chemical reactivity, and molecular solvation phenomenon. 

In the present work, the concentration effect has been correlated with the preferential solvation phenomenon. Eirst, the observed non-exclusion mechanism has been quantified by means of the distribution coefficient, Kp, representing the concentration ratio of macromolecules inside the pores (i.e., in the quasistationary phase) to those in the mobile phase. Second, the shifts in the elution volume owing to either adsorption or, on the contrary, incompatibility of the solute with the gel packing, have been related to the preferential or selective sorption phenomenon. From a thermodynamic viewpoint, the... 

The preferential solvation phenomenon in a ternary polymer system indicates which component, (1) or (2), is preferentially adsorbed by component (3) it is quantified by means of the preferential solvation coefficient, A. From a chromatographic point of view, adsorption or, conversely, incompatibility between solute (2) and gel matrix (3) can be detected through the coefficient K, as seen before. Therefore, both parameters, A and Kp, have a similar physical meaning in the sense that an equilibrium between a binary and a ternary phase is estabhshed and, consequently, one could try to relate them. Accordingly, it is expected that when ATp > 1 [meaning compatibility between polymer (2) and gel matrix (3)], values of A < 0 will be obtained, denoting a preferential solvation of... 

Mis close to the defmitiiHi of the solvation phenomenon. The second case is significantly different, and the name shellvation has been proposed to reflect its unique features. 

The simplest nontrivial solvation phenomenon is the case of a hard-sphere (HS) particle in a fluid of HS particles. This case was discussed in connection with the scaled-particle theory in section 5.11. Here we note that the solvation Gibbs energy of an HS solvaton in an HS solvent is always positive, and it increases monotonically as a function of the size of the HS solvaton or, equivalently, the radius of the corresponding cavity (see section 5.11). 

The increase in activity coefficients originates from a solvation phenomenon. It is now a solute-solvent interaction that is added to the preceding solute-solute interaction. The higher the solute concentration is, the fewer sufficient solvent molecules required to achieve the solute solvation. 

While up to a certain degree solute-induced effects occur in all types of (nonideal) solutions, its manifestation in electrolyte systems deserves special attention. The presence of charged species in a dielectric solvent adds an important ingredient to the solvation phenomenon, i.e., the possible formation of neutral ion pairs. In fact, an outstanding property of water as a solvent at normal conditions is its intrinsic ability to solvate, and consequently dissolve, ionic and polar species, owing to its unusually large dielectric constant. This solvation process is typically described in terms of ion-solvent interactions, ion-induced solvent microstructural changes, solvent dielectric behavior, and their effects on the macroscopic properties of the solution. ... 

Treiner, C., Chattopadhyay, A.K., Bury, R. Heat and solution of various alcohols in aqueous micellar solutions of hexadecyltrimethylammonium bromide as a function surfactant concentration the preferential solvation phenomenon. J. Colloid... 

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