Tools for Investigating Solvation

The more recently used methods for investigating the structure of the region around the ion are listed (though not explained) in Table 2.2. It is convenient to group the methods shown there as follows. 

Several methods involve a study of the properties of solutions in equilibrium and are hence reasonably described as thermodynamic. These methods usually involve thermal measurements, as with the heat and entropy of solvation. Partial molar volume, compressibility, ionic activity, and dielectric measurements can make contributions to solvation studies and are in this group. 

Transport methods constitute the next division. These are methods that involve measurements of diffusion and the velocity of ionic movement under electric field gradients. These approaches provide information on solvation because the dynamics of an ion in solution depend on the number of ions clinging to it in its movements, so that knowledge of the facts of transport of ions in solution can be used in tests of what entity is actually moving. 

A third group involves the spectroscopic approaches. These are discussed in Section 2.11. 

Finally, computational approaches (including the Monte Carlo and molecular dynamic approaches) are of increasing importance because of the ease with which computers perform calculations that earlier would have taken impractically long times. 

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Spectroscopic methods, molten salts, 702 Spectroscopy detection of stmctnral nnits in liquid silicates, 747 and structure near an ion, 72 Standard partial gram ionic entropies, absolute, II Thermodynamics, applied to heats of solvation, 51 of ions in solution, 55 Time average positions of water near ions. 163 Tools, for investigating solvation, 50 Transformation, chemical, involving electrons, 8 Transition metals... 

The modern developments of solvation theory will not be discussed at this point because nearly all the tools for investigating the ion-solvent interaction have become available since 1933. One has to see some of the information they have provided before ion-solvent interactions can be worked out in a more quantitative way. 

Pulse radiolysis is a powerful tool for the creation and kinetic investigation of highly reactive species. It was introduced to the field of radiation chemistry at the end of the 1950s and became popular in the early 1960s. Although the objects of this modern technique were, at first, limited to solvated electrons and related intermediates, it was soon applied to a variety of organic and inorganic substances. As early as 1964, ionic intermediates produced by electron pulses in vinyl monomers were reported for the first time. Since then, the pulse radiolysis method has achieved considerable success in the field of polymer science. 

Time-resolved spectroscopic techniques are important and effective tools for mechanistic photochemical studies. The most widely used of these tools, time-resolved ultraviolet-visible (UV-Vis) absorption spectroscopy, has been applied to a variety of problems since its introduction by Norrish and Porter [1] over 50 years ago. Although a great deal of information about the reactivity of organic photochemical intermediates (e.g., excited states, radicals, carbenes, and nitrenes) in solution at ambient temperatures has been amassed with this technique, only limited structural information can be extracted from such investigations because absorption bands are usually quite broad and featureless. Questions of bonding, charge distribution, and solvation (in addition to those of dynamics) are more readily addressed with time-resolved vibrational spectroscopy. 

The ionic liquids investigated display similar solvation properties for the molecular dipoles, and the choice of anion can be singled out as the main tool to tune the solvation by this means. From the combination of the results of this set of ionic liquids, [C.mpyr CII. S04 is predicted as the ionic liquid most capable to interact with dipoles. On the other hand, [Cnquin]Cl would exhibit the least tendencies in this respect. 

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