Extent of solvation

The solvated sulfenamides [Li2( BuNSC6H4Me-4)2(THF)n] (n = 2,4) have dimeric structures with a central Li2N2 ring. The coordination mode is determined by the extent of solvation of the Li" ions monosolvation allows for rj -N,S coordination whereas disolvation restricts the coordination mode to // -M Variable temperature NMR studies indicated that a dynamic exchange between these two structural types occurs in THF solution (Scheme 10.10). The dihapto coordination mode is observed exclusively in transition-metal complexes and the... 

All electrochemical techniques measure charge transferred across an interface. Since charge is the measurable quantity, it is not surprising that electrochemical theory has been founded on an electrostatic basis, with chemical effects added as a perturbation. In the electrostatic limit ions are treated as fully charged species with some level of solvation. If we are to use UHV models to test theories of the double layer, we must be able to study in UHV the weakly-adsorbing systems where these ideal "electrostatic" ions could be present and where we would expect the effects of water to be most dominant. To this end, and to allow application of UHV spectroscopic methods to the pH effects which control so much of aqueous interfacial chemistry, we have studied the coadsorption of water and anhydrous HF on Pt(lll) in UHV (3). Surface spectroscopies have allowed us to follow the ionization of the acid and to determine the extent of solvation both in the layer adjacent to the metal and in subsequent layers. 

The foregoing sections have dealt with the nucleophilic properties of anionic species whose salts were solubilized in apolar solvents with the aid of cation-complexing agents. Apart from the nucleophilic character of the anion, however, its basic strength is also expected to increase with decreasing extent of solvation. This section will deal with hydrogen-abstraction reactions of crown ether-solubilized bases. 

There are few studies of the effect of temperature on monomer reactivity ratios [Morton, 1983]. For styrene-1,3-butadiene copolymerization by r-butyllithium in rc-hexane, there is negligible change in r values with temperature with r — 0.03, r2 = 13.3 at 0°C and n = 0.04, r% = 11.8 at 50°C. There is, however, a signihcant effect of temperature for copolymerization in tetrahydrofuran with r — 11.0, r2 = 0.04 at —78°C and r — 4.00, r2 = 0.30 at 25° C. The difference between copolymerization in polar and nonpolar solvents is attributed to preferential complexing of propagating centers and counterion by 1,3-butadiene as described previously. The change in r values in polar solvent is attributed to the same phenomenon. The extent of solvation decreases with increasing temperature, and this results in... 

F ure 4.20 Variation of intrinsic viscosity of aqueous protein solutions with axial ratio and extent of solvation. Reprinted, by permission, from P. Hiemenz, Polymer Chemistry, p. 598. Copyright 1984 by Marcel Dekker, Inc. 

Formally, p bh values obtained through Eq. (39) are preferable to those derived from Eq. (37). In fact, the results obtained by both methods are quite similar. On the other hand, Scorrano, Arnett (76APO(13)83) and co-workers have shown that (p is useful in its own right it can be related to the extent of solvation of the neutral and the ionized forms. 

The gas-phase model would then be tested on condensed phases. In the case of the carbonate ion, the parameters can be used to examine the structure of C02(aq), C032-(aq), and HC03 (aq) as well as the structure of, for example, siderite FeC03 and nahcolite Na(HC03). For the aqueous species, the most instructive comparisons are with the results of ab initio molecular dynamics studies of solvated ions, where the radial distribution functions can be used to check the extent of solvation. Fig. 2, for... 

There is little correlation of the AG (Tr) values with the parameters e and /(U7Sn-H), although the free energy of the transition states tends to be lower when the values of /(U7Sn-H) are higher (especially when aprotic solvents alone are considered). If, indeed, /(117Sn-H) does measure the extent of solvation at... 

Since the reactants are molecules, the extent of solvation will be small and approximately the same for all solvents. But the extent of charge separation in the activated complex is very dependent on the solvent, by virtue of the magnitude of the relative permittivity, and a large variation in the extent of solvation of the activated complex is expected. The entropy of activation and the A factor are expected to vary with change of solvent. 

Note from Table 6.8 that the reduced viscosity gives the relative increase in the viscosity of the solution over the solvent, per unit of concentration. Since r/ is the limiting value of the reduced viscosity, it is a measure of the first increment of viscosity due to the dispersed particles and is therefore characteristic of the particles. Equation (6.33) predicts that the intrinsic viscosity should equal 2.5 for spherical particles. If the dispersed phase volume fraction is used to reflect the dry-weight concentration of particles that may become solvated when dispersed, then intrinsic viscosity measurements can be used to determine the extent of solvation as follows. Suppose the mass of colloidal solute in a solution is converted to the volume of unsolvated material using the dry density. If the particles are assumed to be uniformly solvated throughout the dispersion then the solvated particle volume exceeds that of the unsolvated particle volume by the factor 1 + (m], b/m2)(p2/Pi) where my, is the mass of bound solvent, m2 is the mass of the solute particle, p2 is the density of the particle and pi is the density of the solvent. Since 4>[Pg.185]

On the other hand, does the formula H30+ give sufficient expression to the extent of solvation of the aqueous hydrogen ion There is persuasive evidence that the formula H904+ (1), with three further molecules of water of solvation, is a better representation of the hydrogen ion in solution than Hs0+ (Eigen, 1963). Such a formula would imply... 

Inevitably this specific electrophilic solvation must be included in the Y, Z and T scales of solvent ionizing power. Ideally some correction for the different extents of solvation of the anions Cl-, OTs-, I-) should be made, and then the various scales of solvent polarity may be more comparable. 

Other. Most drug substances used to manufacture dosage forms are solids. It is therefore necessary to consider other properties that may affect the bioavailability with the possibility of eliciting adverse reactions. These parameters, which should be adequately addressed both in the specifications and in the characterization/structure elucidation section, include the nature and extent of solvation, the possibility of different polymorphs, and particle size. 

The extent of solvation is routinely monitored by LOD testing conducted at a temperature previously defined by TGA. Either the basis for concluding the existence of only one solvated form or information comparing the respective solubilities, dissolution rates, and physical/chemical stability of the different solvates should be provided. 

Examples of published spectra were for Ni2+ and Co2+ [27], Mn2+ and Cr3+ [28] and Pr3+ and Nd3+ [27]. In all cases comparison of HF solution spectra with those in acidic aqueous solutions indicated that the extent of solvation by HF was identical for each cation with that by H20. Spectra of cationic species in HF, usually [M(HF)6]"+, are simpler than those in water where many species such as Cl-can enter the coordination sphere to form, in the simplest case, [M(H20)5C1](,-I)+. The only anions other than F- in HF are the conjugate anions of the Lewis acids, e.g. BF4, SbFg, etc, which coordinate extremely weakly and have not been observed spectroscopically in the coordination sphere of metal cations in HF solutions. 

The propagating anion and its counterion exist in relatively nonpolar solvents mainly in the form of associated ion pairs. Different kinds of ion pairs can be envisaged, depending on the extent of solvation of the ions. As a minimum, an equilibrium can be conceived between intimate (contact) ion pairs, solvent-separated ion pairs, and solvated unassociated ions. The nature of the reaction medium and counterion strongly influences the intimacy of ion association and the course of the polymerization. In some cases the niicrostructure of the polymer that is produced from a given monomer is also influenced by these variables. In hydrocarbon solvents, ion pairs are not solvated but they may exist as aggregates. Such inter-molecular association is not important in more polar media where the ion pairs can be solvated and perhaps even dissociated to some extent. 

Hence ihe basicity of the amines is enhanced in proportion to the extent of solvation of ttie mnjiiEarp ammonium ion. and the energies of solvation are RNHj > >... 

The dry state morphology obtained from gas sorption experiments does not reveal how the material interacts with solvents. In addition to the measurement of swelling and solvent uptake, fluorescent probes can be incorporated in the polymer network and used to measure the extent of solvation of the polymer in a given solvent [51,54]. For this purpose Shea and co-workers incorporated dansyl... 

From a chemical point of view the support must be chemically inert to all the reagents and solvents used for peptide synthesis but, at the same time, must be reactive enough to allow the covalent attachment of the first amino acid of the sequence to be synthesized. However, the most important consideration for a successful solid-phase synthesis is, probably, the extent of solvation and swelling of the peptide resin in the reaction medium.In general, maintenance of a highly swollen state of the peptide resin throughout the synthesis is a requirement for rapid and complete chemical reactions. 

Thermogravimetric analysis (TGA) Solvates, hydrates. Can be used to determine extent of solvation. 

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