Solvation group additivity

The equilibrium constants in Table 22 suggest that the larger the peri substituent, the less favored is the sc form. Since the phenyl group takes a conformation in which it does not directly interact with the peri CH group, this result may originate in the ease or difficulty of solvation in addition to an entropy factor due to limitations of certain conformations. 

Fe(5N02phen)3] + aquation in ternary water-Bu OH-polyethyleneglycol (PEG400). " Kinetic patterns for systems of these types have been the subject of theoretical analyses, as in the application of the Savage-Wood Group Additivity principle to [Fe(5N02phen)3f" " aquation in a variety of water-rich binary aqueous mixtures and in aqueous salt solutions " and in the Kirkwood-Buff treatment of preferential solvation of initial and transition states for [Fe(phen)3] + aquation in methanol-water " and for [Fe(gmi)3] " " aquation in Bu OH + water. " ... 

Useful source of information on the calculation of energy quantities heats of formation, reaction energies, bond energies, activation energies, etc. Methods group additivity, molecular mechanics, semiempirical, DFT, and high-accuracy ab initio (G2, CBS, etc.) energies of solvation. 

As was the case with chiral shift reagents, preferential population of one diastereomer over the other (Kr Ks) is not a prerequisite for induced anisochrony of enantiotopic groups. Additionally, since the CSA is diamagnetic, it may be used in excess over the analyte. A five-fold excess is usually sufficient to drive the equilibria of Equation 2.16 to the outside, such that the solute is present only as its two diastereomeric solvates. Since the observed spectra are time-averages of all the species in solution, this chemical trick simplifies analysis of absolute configuration by focussing on the diastereomeric solvates alone. 

Figure 4. Mechanistic scheme for reactions in proteins initiated by solvated electron addition to the carbonyl group in the peptide backbone.

The solvation Gibbs energies of dihydroxybenzene were calculated by Censky et al. (2007) based on the assumption of group additivity. This assumption is not supported by theory, but it seems to work quite well. 

Note, however, that in Table 12 of Censky et al. (2007), there are also values of the solvation Gibbs energies of diaminobenzene. All three isomers have the same values. This is an indication of the failure of the group additivity assumption for these cases. 

Conditional Solvation Helmholtz Energy Group Additivity... 

Researchers in solvation thermodynamics have long attempted to assign group contributions of various parts of a solute molecule to the thermodynamic quantities of solvation. In this section we examine the molecular basis of such a group-additivity approach. As we shall see, the problem is essentially the same as that treated in the previous section i.e., it originates from a split of the solute-solvent intermolecular potential function into two or more parts. 

In (8.9,16) the solvation Gibbs energy of M is divided into two parts. We transfer first the tail group and then the head group, given the condition that the tail group has already been solvated. We can make the same transfer in a different order, as in Eq. (8.9.17), but the first seems to be more useful for the present case. Note that both (8.9.16) and (8.9.17) are exact and do not involve the assumption of group additivity (see also section 8.14). Similarly, for any A we write... 

Example Solvation can have a profound effect on the potential energy profile for a reaction. Jorgensen s research group provided important insights into the role of solvation. Consider the nucleophilic addition of the hydroxide anion to formaldehyde ... 

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