Ion thermodynamics

The Kolbe-Schmitt reaction is an equilibrium process governed by thermodynamic control The position of equilibrium favors formation of the weaker base (salicylate ion) at the expense of the stronger one (phenoxide ion) Thermodynamic control is also responsible for the pronounced bias toward ortho over para substitution Salicylate anion IS a weaker base than p hydroxybenzoate and predominates at equilibrium... 

Sufficient stability of the hydrocarbon ions, as the salt or in the solution, is an obvious prerequisite for these procedures, and, in practice, selecting or designing the stable ions and choosing a proper solvent are tasks of primary importance. As an ordinary stability index for the ions, thermodynamic scales referred to the water molecule, i.e. p CR+ and pKa values, are chosen for the carbocation and carbanion, respectively. 

This ion, thermodynamically a powerful oxidant , is reduced by comparatively few reagents. However, both V(II) and V(III) are effective , viz. 

Plutonium(IV), hydrolysis of, 19 698 Plutonium-231, 19 670 Plutonium-238, 19 668, 669, 675 special precautions for, 19 703 Plutonium-239, 19 669 Plutonium aqua ions, thermodynamic values for, 19 693t Plutonium carbide, 4 649t stoichiometry, 4 651 Plutonium carbide (2 3), 4 649t Plutonium carbides, 19 690-691 Plutonium cations, 19 692 Plutonium chalcogenides, 19 691 Plutonium complexes bonding in, 19 694—695 formation constants for, 19 697t... 

Moreover, the peaks of the E series in the mass spectra of furanoses have an increased intensity, the fission of the side chain from the five-membered ring leading to planar oxinium ion, thermodynamically favored over the analogous ion having a six-membered ring. ... 

Although analysis in terms of short-lived carbanions fits the stereochemistry discussed up to now, the results should not be taken as indicative of short-lived ions. Thermodynamic control via long-lived carbanions will give the same results, as was actually suggested by Truce and coworkers. 

Example 2.10 Is the reaction between metallic Fe and a 1 M solution of a strong (non-oxidizing) acid to produce Fe2+ ions thermodynamically spontaneous ... 

It is noteworthy that most ofthe complexes formed are actually mixed ligand complexes whereby two different ligands are associated with the same metal ion. Thermodynamically, these form the more stable complexes. 

Not only is the uranyl ion thermodynamically robust, it is also kinetically inert. Experiments designed to measure the rate of isotopic oxygen exchange between the oxo atoms and water at room temperature, establish that the exchange half-life is greater than 40,000 hours [19]. This overall chemical stability accounts for an extensive coordination chemistry which is exploited, for example, in the solvent extraction separation processes used in the nuclear fuel cycle [20]. 

Dissociation Constant in Aqueous Phase. In general, in any solvent, there can be free ions (thermodynamically distinct entities) coexisting in equilibrium with ion pairs. Often, it is assumed that the quat is completely ionized in the aqueous phase to form free ions. However, this assumption may not be valid in all cases and, in general, a dissociation constant can be defined as... 

The behavior of the fluoride ion is qualitatively different. The solvent interactions stabilize the ion thermodynamically in the range from -8 to -5 A, whereas the solvent effect is mostly repulsive for (and Cl ). For F the attraction by the layer of adsorbed water (which are oriented preferentially with the hydrogen atoms pointing into the solution) appears to dominate over the steric repulsion. The distance of the minimum (at about 5.5 A) corresponds to an adsorbed species F (H20)6 or F (H20)y on top of the adsorbed layer of water molecules. A detailed analysis [196] shows that the very strong repulsion at distances below 5 A is due to hydration. 

In a most recent paper,a new table of absolute single-ion thermodynamic quantities of hydration at 298 K has been presented, based on conventional enthalpies and entropies upon implication of the thermodynamics of water dissociation. From the values of AiydG the Bom radii were calculated from... 

Kezic, B. and A. Perera. 2011. Towards a more aceurate reference interaction site model integral equation theory for molecular liquids. Journal of Chemical Physics. 135, 234104. Kim, J. I. 1978. A critical study of the Ph4AsPh4B assumption for single ion thermodynamics in amphiprotic and dipolar-aprotic solvents Evaluation of physical parameters relevant to theoretical consideration. Zeitschriftfur Physikalische Chemie. 113,129. 

Porous silicon readily undergoes oxidation in aqueous solution. Electrons formed by the oxidation reduce metal ions thermodynamically, if the equilibrium potential stays positive compared with the potential of reaction (2). 

There is a wealth of information on gas phase ion thermodynamics because of the power of mass spectrometry and ion cyclotron resonance techniques. Before we discuss carboca-tion, and subsequently carbanion, stabilities, keep in mind that ionic structures are much more sensitive to environmental influences than radicals. The polarity, nucleophilicity, and hydrogen bonding ability of the solvent are important influences, as are the nature of the counterion. As such, thermodynamic information is a less reliable predictor of reactivity for carbocations and carbanions than it is for radicals. Nevertheless, gas phase thermodynamics is an excellent starting point, defining the intrinsic stabilities of ions. Any deviation in trends between gas phase and solution studies is likely a consequence of solvation effects, a theme we will visit many times throughout this book. 

Saladini M, Menabue L, Ferrari E (2001) Sugar complexes with metaF+ ions thermodynamic parameters of associations of Ca, and Zn + with galactaric acid. Carbohydr Res 336(1) 55-61. doi 10.1016/S0008-6215(01 )00243-9... 

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