Solvation rule

This solvation rule for 5n2 reactions can be useful in predicting the influence of a change in solvent on the structure of activated complexes. It is in agreement with studies involving leaving group heavy atom and secondary a-deuterium kinetic isotope effects, as well as theoretical calculations of solvent effects on transition-state structures. Possible limitations of this solvation rule have been discussed see [498] and relevant references cited therein. 

Finally, it is worth noting that the different transition state structures suggested by the secondary a-deuterium and nitrogen KIEs measured in methanol and in DMF are consistent with the Solvation Rule for Sn2 Reactions 96 which predicts that the transition state for this Type II SN2 reaction will be very solvent dependent. 

Other studies of mononuclear gold catalysis with AuBr [66], as well as AuCl and AuClg [67], using standard DFT approaches with solvation, ruled out pathways... 

It was possible to formulate a rule describing how the copolymerization parameters depend on the polarity of the solvent used. This rule is a result of contemplation about the connection between the copolymerization parameters and propagation rate constants during the cationic polymerization as well as about the changes of solvation of educts and activated complexes of the crossed propagation steps in solvents with varied polarity 14 U7). The rule is as follows ... 

At this stage of development of the subject it is appropriate to consider a number of empirical rules which may serve to indicate the important variables. It would seem likely that (i) there will be competitition between each species in the system for the sites available at the electrode surface, and that (ii) for each species in the system there will be an equilibrium between the solution and the adsorbed state. Thus it would be expected that the solution constituents would affect these equilibria in two ways (a) if one of the constituents of the medium is itself adsorbed, the reactant will tend to be displaced (b) if the reactant is strongly solvated, complexed or ion paired by constituents of the medium, the species in solution will be favoured. 

The values of hj for different ions are between 0 and 15 (see Table 7.2). As a rule it is found that the solvation number will be larger the smaller the true (crystal) radius of the ion. Hence, the overall (effective) sizes of different hydrated ions tend to become similar. This is why different ions in solution have similar values of mobilities or diffusion coefficients. The solvation numbers of cations (which are relatively small) are usually higher than those of anions. Yet for large cations, of the type of N(C4H9)4, the hydration number is zero. 

As we can see from the last entry in this table, we have deduced only a rule. In InBi there are Bi-Bi contacts and it has metallic properties. Further examples that do not fulfill the rule are LiPb (Pb atoms surrounded only by Li) and K8Ge46. In the latter, all Ge atoms have four covalent bonds they form a wide-meshed framework that encloses the K+ ions (Fig. 16.26, p. 188) the electrons donated by the potassium atoms are not taken over by the germanium, and instead they form a band. In a way, this is a kind of a solid solution, with germanium as solvent for K+ and solvated electrons. K8Ge46 has metallic properties. In the sense of the 8-A rule the metallic electrons can be captured in K8Ga8Ge38, which has the same structure, all the electrons of the potassium are required for the framework, and it is a semiconductor. In spite of the exceptions, the concept has turned out to be very fruitful, especially in the context of understanding the Zintl phases. 

It follows from Eqs. (2.6.6), (2.6.8) and (2.6.10) that the presence of the solvent has two effects on the ionic mobility the effect of changing viscosity and that of changing the ionic radius as a result of various degrees of solvation of the diffusing particles. If the effective ionic radius does not change in a number of solutions with various viscosities and if ion association does not occur, then the Walden rule is valid for these solutions ... 

Although it is very hard to observe the absorption spectrum of eh when metal is dissolved in water because of its high reactivity, some attempts were made in water and ice (Jortner and Stein, 1955 Benett et al., 1964, 1967). Furthermore ESR (electron spin resonance) studies revealed that the trapped or solvated electron in ice interacts with six equivalent protons, thus ruling out H20-. 

One of the simplest applications of the HSAB principle is related to solubility. The rule "like dissolves like" is a manifestation of the fact that solute particles interact best with solvent molecules which have similar characteristics. Small, highly charged particles or polar molecules are solvated best by solvents containing small, highly polar molecules. Large solute particles having low polarity are solvated best by solvent molecules having similar characteristics. Consequendy, NaCl is soluble in water, whereas sulfur, S8, is not. On the other hand, NaCl is insoluble in CS2, but S8 dissolves in CS2. 

Kamlet, M. J., Doherty, R. M., Carr, P. W., Mackay, D., Abraham, M. H., Taft, R. W. (1988) Linear solvation energy relationships. 44. Parameter estimation rules that allow accurate prediction of octanol/water partition coefficients and other solubility and toxicity properties of polychlorinated biphenyls and polycyclic aromatic hydrocarbons. Environ. Sci. Technol. 22, 503-509. 

---