Conditional solvation definition

In the aforementioned examples, the conditional solvation Helmholtz energy includes the direct interaction between the two solute particles, as well as the effect of the solvent. In some applications it is found useful to exclude the direct interaction. This occurs whenever we want to estimate the contributions to the solvation Helmholtz energy of each part of a combined solute. In our definitions of both AA (Ri) and AA (R2/Ri ), we transferred one solute s from a fixed position in an ideal gas into the liquid. Now suppose that we are given a pair of solutes at a distance R = R2 — J i in an ideal gas. This pair of solutes can be viewed as a single molecule. We wish to know the contribution of each particle (1 and 2) to the Helmholtz energy of solvation of the pair. The latter is... 

In Fig. 3.3, we also show the process that we shall refer to as the conditional solvation process. The definition of the two processes is the same except that in the conditional process we transfer s to a fixed point in a liquid adjacent to some molecule referred to as the backbone BB). Clearly, if the backbone perturbs the distribution of solvent molecules around it, the conditional solvation thermodynamic quantities will be different from the corresponding solvation quantities. 

We recall the definition of the conditional solvation Gibbs energy of a FG, k, in a polymer a ... 

Remarkable data on primary hydration shells are obtained in non-aqueous solvents containing a definite amount of water. Thus, nitrobenzene saturated with water contains about 0.2 m H20. Because of much higher dipole moment of water than of nitrobenzene, the ions will be preferentially solvated by water. Under these conditions the following values of hydration numbers were obtained Li+ 6.5, H+ 5.5, Ag+ 4.4, Na+ 3.9, K+ 1.5, Tl+ 1.0, Rb+ 0.8, Cs+0.5, tetraethylammonium ion 0.0, CIO4 0.4, NO3 1.4 and tetraphenylborate anion 0.0 (assumption). 

The Chemical Reactivity of e aq. The chemical behavior of solvated electrons should be different from that of free thermalized electrons in the same medium. Secondary electrons produced under radio-lytic conditions will thermalize within 10 13 sec., whereas they will not undergo solvation before 10 n sec. (106). Thus, any reaction with electrons of half-life shorter than 10 n sec. will take place with nonsolvated electrons (75). Such a fast reaction will obviously not be affected by the ultimate solvation of the products, since the latter process will be slower than the interaction of the reactant with the thermalized electron. This situation may result in a higher activation energy for these processes compared with a reaction with a solvated electron. No definite experimental evidence has been produced to date for reactions of thermalized nonsolvated electrons, although systems have been investigated under conditions where electrons may be eliminated before solvation (15). 

Local density enhancements, being by definition short-ranged, are not peculiar to the highly compressible near-critical region. Very close to the solute molecule, the local environment differs markedly from the bulk (for example, the local density in the first solvation shell at bulk near-critical conditions is p (R) = 1.43 pc when p = 0.31 and T/Tc = 1.02). However, even this region does not appear to have a liquid-like character, as suggested by other spectroscopic experiments (35-36),... 

If the reaction mixture is very dilute in the reactants and the products, the activity coefficients can all be approximated by unity. Then the last term on the right hand side of Eq. (2.20) vanishes, and the left hand side can be written as AG° = -RT n ATsolution, the equilibrium quotient becoming the equilibrium constant. Under ordinary conditions, however, the activity coefficient term must be taken into account, since there are solvent effects on all the terms on the right hand side except -RTIn K". The fact that different numbers of solvent molecules may specifically associate with the reactants and the products and that solvent molecules may be released or consumed in the reaction should not be included explicitly, since this effect is already covered by the terms in AG s of solvation of the reactants and products according to our definition of this concept. 

For some compounds, suitable crystals simply can not be obtained and all attempts are frustrated. The reasons are not well understood. In some cases, repeated attempts with varied conditions always produce multiple or twinned crystals. Trying a range of different solvents is the most obvious approach. It is not just that the crystal quality may vary with the solvent used incorporation of solvent in the crystal structure generates a different crystalline form (a solvate), which will probably have quite different crystal growth characteristics. In most cases the nature of the solvent is unimportant in the quest for a definitive crystal structure analysis. However, the study of different solvates (and different polymorphs) of the same compound can itself be of interest, with significant changes in molecular structure resulting from different intermolecular interactions. 

This effect must not be confused with the cybotactic effects we have mentioned, nor with the hole in the solute-solvent correlation function gMs(t) (see Figure 8.5). The hole in the radial correlation function is a consequence of its definition, corresponding to a conditional property, namely that it gives the radial probability distribution of the solvent S, when the solute M is kept at the origin of the coordinate system. Cybotactic effects are related to changes in the correlation function gMs(t) (or better gMs(r> )) with respect to a reference situation. Surface proximity effects can be derived by the analysis of the gMs(r,fi) functions, or directly computed with continuum solvation methods. It must be remarked that the obtention of gMs(r) functions near the surface is more difficult than for bulk homogeneous liquids. Reliable descriptions of gMs(ri re even harder to reach. 

Not only rigidness can be important for chirality. Indeed, the definition pass over observation time scale, physical conditions (temperature, pressure), state of aggregation, solvation, isotopic composition etc. which are, for obvious reasons, important for chirality of molecules. The time scale is especially crucial for spectroscopic observations of non-rigid chiral molecules, because, the effects observed. 

Several groups have correctly noted that there is no universally accepted definition of cocrystal and then proceed to circumspectly state merely what they understand it to be. In an attempt to exclude solvates (and hydrates), Zaworotko and coworkers have stated that they and others have operated under the assumption that a cocrystal is a multiple component crystal in which all components when pure are solid under ambient conditions. Aakerdy and Salmon delineated the following three criteria to which they subscribe ... 

Crystal engineering is a scientific area in constant flux, which helps explain why unambiguous definitions have not yet been developed and/or accepted. The term cocrystal is not well defined, and the existing literature contains terms such as molecular complexes, multicomponent solids, cocrystals, molecular adducts, molecular salts, clathrates, and inclusion compounds that frequently describe one and the same family or type of chemical compounds. We will not attempt to add to the ongoing discussion, and we limit our overview to structurally homogeneous crystalline materials containing two or more neutral building blocks that are present in definite stoichiometric amounts and that are made from reactants that are solids at ambient conditions [1] (therefore hydrates and other solvates are excluded from this overview). In addition, we do not discuss... 

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