Iso-solvation

A convenient measure of the degree of selective solvation is the bulk solvent composition at which both solvents of a binary mixture participate equally in the contact solvation shell. This is the solvent composition at which the NMR chemical shifts lie midway between the values for the two pure solvents. This composition has been called the equisolvation or iso-solvation point (usually expressed in mole fractions of one solvent) [125]. According to Fig. 2-10, this point describes the bulk solvent composition at which both solvents A and B participate equally in the solvation shell of the cation or the anion, respectively. 

A useful probe of the immediate chemical environment of solute ions is the NMR chemical shift of alkali metal ions obtained in binary solvent mixtures [111, 126, 295]. These measurements are based on the assumption that the chemical shift of the solute cation is determined in an additive fashion by the solvent molecules comprising the first solvation shell. For example (cf. Fig. 2-11), the iso-solvation point of Na in dimethyl sulfoxide/acetone mixtures occurs at xxO.21 cmol/mol dimethyl sulfoxide, indicating the higher solvating ability of this solvent relative to acetone. As shown schematically in Fig. 2-11, the preferential solvation of Na by dimethyl sulfoxide displaces its chemical shift towards <5dmso and a deviation from the straight line is observed. 

TABLE 6.5 The Iso-solvation Points Equaling the Local Mole Fractions for Sodium Ions in Binary Mixtures of Solvents A and B°... 

Inductive effects on dipole moments and the effects of intervening atoms on electrostatic interaction energies are represented by polarizability centers In conjunction with bond centered dipoles. Solvation energies are estimated by means of a continuum dlpole-quadrupole electrostatic model. Calculated energies of a number of conformations of meso and racemic 2,4-dichloropentane and the iso, syndio, and hetero forms of 2,4,6-triehloroheptane give satisfactory representations of isomer and conformer populations. Electrostatic effects are found to be quite important. 

Hexyl alcohol, a mixture of n- and iso C6 alcohols made via the oxo process by Exxon Chemical Co., started the flow of new monohydric alcohols as intermediates for PVC plasticizers in the sixties. Dihexyl phthalate - the phthalate of this alcohol - is a fast solvator and competes with other fast solvating types in markets such as vinyl flooring and carpet backing. 

The hexameric scandium decanoate extracted in benzene is different from the hexameric Al(III), Ga(III), and In(III) decanoates in that the former is neither hydrated nor hydrolyzed (154). Galkina and Strel tsova (36), in the butanoic acid/iso-butanol system, attempted to separate Sc from rare earths and the other metals. They proposed the monomeric Sc(III) butanoate, ScA3, as the extracted species. In this extraction system, the polymerization of scandium butanoate in the organic phase seems to be prevented by solvation with iso-butanol. In the study of the synergistic effect of various amines on the extraction of lanthanum and scandium with hexanoic and a-bromohexanoic acids in chloroform, Sukhan et al. (138) proposed LaA3(HA)3 and ScA3(HA)3 as the extracted species. 

AG gi = 2(yi-s) Iso holds well for ion solvation energies. Clearly, there... 

These types are not all sharply divided, but many compounds may be considered to belong to two or more of these classifications. Although schemes of nomenclature are available for all of these types, the schemes are reasonably satisfactory for only three (solvates, double salts, and iso- and heteropoly acids and salts). This situation is the more regrettable because so large a proportion of the total number of known compounds belongs to the class of higher order compounds and modem research is rapidly enlarging both the number and complexity. 

For the [Anm(Cot)2] anions magnetic moment measurements have been carried out for the Np, Pu, and Am derivatives (63, 64), all in the form of the 2 THF solvates. Thus X-ray diffraction data show that KNp(Cot)2 2 THF and its Pu and Am analogues are all iso-structural, and similar results for the related diglyme solvates indicate that it is extremely probably that these are iso-structural with the salt KCe(Cot)2 diglyme, which is known (23) to have a sandwich structure with D8d symmetry about the Ce atom. Consequently it is reasonable to assume that the pseudo-axial ligand field model is applicable to these [Anin(Cot)2] systems, and to interpret the magnetic data in these terms. 

The 7Li chemical shifts for iso-HMTT LiBr in this mixed solvent system are very strongly correlated with the N-CH2 H chemical shifts at higher concentrations of iso-HMTT LiBr. At low concentrations, however, the upfield 7Li chemical shift reaches a maximum and then decreases. This behavior is even more striking in the case of PMDT LiBr in benzene shown in Figure 10. The divergent behavior of the H and 7Li chemical shifts at very low concentration of Chel LiBr may be evidence that a second type of benzene solvation occurs in monomeric Chel LiBr. We speculate that this may be evidence of benzene solvar tion in the vicinity of the anion. 

Anions from the Schiffs base (78) can be C- or A -alkylated with ethyl iodide or diethyl sulphate. The ratio of the products depends both on the solvent and on the presence of 18-crown-6. In non-polar solvents, the crown ether increases the solubility of the base, and C-alkylation is the major pathway. In dipolar aprotic solvents, the 18-crown-6 breaks up ion pairs by solvation of the Na" cation, and favours A -alkylation. A nerylsulphonamide, formed from (79), undergoes regiospecific reductive desulphonylation to give nerol (80), which implies that (79) is an effective synthon for cisoid iso-prenoids. Chiral complexes of crown ethers, e.g. (81), catalyse the Michael addition reaction of j3-keto-esters and methyl vinyl ketone to give adducts in high optical yields. ... 

The first method is based on the statistical distribution of an iso-topically-labelled solvent such that the ratio of the concentration of isotopic solvent in the coordinated solvent to its concentration in the bulk solvent is equal to the ratio of coordinated solvent molecules to bulk solvent molecules. One obvious requirement is that the half-life of solvent exchange must be considerably longer than the time required for isotopic sampling. Furthermore, there must be an efficient means of separating the coordinated solvent from the bulk solvent. This approach was first used by Hunt and Taube [13] to establish the existence of Cr(H2 0)g as a distinct species in aqueous solution. Although only of limited application to metal ions more labile than Cr the method has been employed to determine the solvation number of the hydrated Al ion using a flow... 

The u.v. and c.d. spectra of (364 R = Me, Et, Pr, Bu , or PhCH2) in EtOH and in iso-octane have been reported.The chiroptical properties of the oxaziridine chromophore were generally characterized by a positive pattern at 190—350 nm. The notable exception to this was a clear negative Cotton effect for (364 R = Pr ). The seemingly anomalous behaviour of this compound was interpreted in terms of the possible existence of solvation equilibria and conformational rotamers about the N—CHMe2 bond. The relatively new technique of Liquid-Crystal-Induced Circular Dichroism (LCICD) has been used in the... 

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