Solvation requirements

Reasonably reliable pATbh+ values for the protonation of weak bases or of weakly basic substrates can be obtained via equation (17), together with m slope parameters that can be used to classify basic molecules as to type, and for an estimate of the solvation requirements of the protonated base. Measurements at temperatures other than 25°C can be handled using equation (22), and enthalpies and entropies for the protonation can be obtained. Protonation-dehydration processes are covered by equation (26). Medium effects on the... 

Thus the free energy of solvation may be calculated from the Henry s law constant or from the vapor pressure of the pure substance and the limiting activity coefficient. Thus, if the deviation of the solution from Raoult s law behavior is known, calculation of the standard state free energy of solvation requires only the vapor pressure of the pure substance (in the standard state... 

One of the major objectives of physical organic chemistry is the detailed description of transition states in terms of nuclear positions, charge distributions, and solvation requirements. A considerable aid to this task is provided for many reaction series by the existence of extrathermodynamic relationships, whose mathematical simplicity largely arises from extensive cancellation of the contribution to the free-energy change from the part of the molecule outside the reaction zone. 

The rate enhancement by anionic micelles is the consequence of a decrease in both the enthalpy and the entropy of activation (Graham and Leffler, 1959), and thus the catalysis is understandable in terms of a greater rate of racemization in the micellar phase than in the bulk solvent resulting from decreased solvation requirements and less destabilization of the transition state in the micellar system relative to that in water. 

Lower water activity in the solution phase may result in the full solvation requirements of ions not being met, thus changing the ion-ion and ion-solvent energetics described for dilute solutions thereby changing the relative affinities. 

The equilibrium between the thermodynamically distinct states will be governed by a delicate balance between the solvation requirements of the ions and the Coulombic interactions 73). One can illustrate two ions, of which at least one has a solvation shell, that approach each other. The potential energy of the system is reduced as the solvation... 

Estimation of the entropy of solvation requires calculation of the entropy of the ion in the gas phase. For a monoatomic ion, the main contribution to the entropy comes from its translational energy. Simple ions formed from the main group elements have the electronic structure of an inert gas and therefore do not have an electronic contribution to the entropy. On the other hand, ions formed from transition metals may have an electronic contribution to the gas phase entropy, which depends on the electronic configuration of the ion s ground state and of any other electronic states which are close in energy to the ground state. The translational entropy is given by the Sackur-Tetrode equation, which is obtained from the solution of the SWE for a particle in a box (see section 2.2)... 

One of the important properties of ionic liquids is that they can be fine-tuned to meet specific solvation requirements to influence reaction outcomes. In recent years, the use of chiral ionic liquids as reaction media for asymmetric organic reactions and chiral discrimination as well as the optical resolution of racemic mixtures has dramatically increased. Unfortunately, there are only a few chiral ionic liquids that are designed, synthesized, and used as solvents for asymmetric reactions, leaving open an important area with huge potential and scope for further development. 

The rate of decarboxylation of 6-nitroindoxazene-3-carboxylic acid is subject to dramatic solvent effects which support the anionic nature of the transition state (38).8,53 The marked acceleration on going from water (rate 7.3 x 10-6sec-1) to a dipolar aprotic solvent (e.g., dimethylformamide, rate 3.7 x 10 sec- ) is interpreted in terms of the different solvation requirements of the carboxylate anion (40), with its comparatively localized charge, and the transition state (38) with its delocalized charge. In protic solvents intermolecular hydrogen bonding with the carboxylate ion inhibits decarboxylation by selectively stabilizing the acid, whereas dipolar aprotic solvents stabilize the transition state (38) and hence accelerate loss of carbon dioxide. 

The data in Table 3 allow consideration of the importance of solvation of the free base. The acidity functions HR and Hc are defined for ionization of triarylcarbinols and of diarylethylenes, respectively. The conjugate acid is, in both cases, the arylcarbonium ion. The ratio 7xh+/Tx is different since the solvation requirements of the free bases are different, with the carbinol being obviously more... 

Ruthenium(iv).—Effects of added ions (H+, Li+, Na+) on the rates of formation of chloride and bromide complexes of ruthenium(iv) can be explained in terms of the effects of the added cations on solvent structure. Their solvation requirements seem to encourage water loss from the co-ordination shell of the ruthenium(iv). ... 

Mixtures of a solvent and a non-solvent (S/N) were used in majority of the cases for tuning of the polymer retention. As shown in Tables 1-3, non solvents are added in amounts from 0.6 to 70%. A decrease in the thermodynamic quality of the mobile phase by adding of the precipitant (non-solvent) is occasionally connected with problems of the poor solubility of higher molar mass samples or even with the inability to reach the critical condition due precipitation of polymer samples. The precipitation may be supported, not only by the high concentration of the non solvent in the mobile phase, but also by high concentration of non solvent adsorbed on the sorbent surface. In mixtures of solvent and precipitant, the extent of the preferential solvation of the polymer coils may be the reason why both solubility and movement of the polymer in solvent/precipitant mixtures are possible. An evaluation of coefficient of preferential solvation requires separate measurements, which have been not performed in connection with CEEC. 

We have compared a series of acetylenes and ethylenes(18) and always found very similar parameters which indicate that the solvation requirements of the two reactions are very similar. Yates has reached similar conclusions(11b) form the evaluation of the transition states activity coefficients, although his computation from our data shows a difference of about 4 kJ mol in the f term. This difference must be, however, somewhat overestimated. In fact, the plot of log ajj+ - log k = log fyt / fgk vs. the medium acidity (see Figure 2) runs parallel for styrene and phenylacetylene in all... 

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