Basicity constant definition

Proton, by definition, is called specific acid, and if the overall energy barrier (activation energy) of a reaction is reduced in the presence of proton as a catalyst, then the reaction is said to involve specific acid catalysis. Generally, catalyst proton reacts with reactant (substrate) in a so-caUed acid-base reaction process, which, in turn, activates the reaction system (by either the preferential destabilization of reactant state or stabilization of transition state in the rate-determining step) for the product formation. The products do not contain any molecular site, which has enough basicity to trap the proton catalyst irreversibly or even reversibly. Thus, for a detectable S A catalysis, the basicity (measured by the magnitude of basicity constant, KJ of the basic site of electrophilic reactant, products, and solvent should vary in the order K, (for electrophilic reactant) > (for solvent) > Kb (for products). 

Table 5.7 lists the nucleophilic constants for a number of species according to this definition. It is apparent from Table 5.7 that nucleophilicity toward methyl iodide does not correlate directly with basicity. Azide ion, phenoxide ion, and bromide are all equivalent in nucleophilicity but differ greatly in basicity. Conversely, azide ion and acetate ion are... 

Attempts have been made to deduce the structure of the predominant form of a potentially tautomeric compound from the shifts which occur in the ultraviolet spectrum of the compound in question on passing from neutral to basic or acidic solutions. The fact that no bathochromic shifts were observed for 2- and 4-hydroxy quinoline and 1-hydroxyisoquinoline under these conditions was taken as evidence that they existed in the oxo form [similar work on substituted quinol-4-ones led to no definite conclusions ]. A knowledge of the dissociation constants is essential to studies of this type, and the conclusions can, in any case, be only very tentative. A further dif-... 

Let us once more consider the basic definition of the equilibrium dissociation constant, Ki, in terms of the rates of binary complex association and dissociation ... 

There are basically two semicontinuum models one owing to Copeland, Kestner, andjortner (1970) (CKJ) and another to Fueki, Feng, and Kevan (1970, 1973 Fueki et al, 1971) (FFK). The calculations were designed for eh and eam,but have been extended to other polar media (Fueki et al., 1973 Jou and Dorfman, 1973). In these four or six solvent molecules form the first solvation layer in definite arrangement. Beyond that, the medium is taken as a continuum with two dielectric constants and a value of VQ, the lowest electron energy in the conduction state. 

VAN AKEN et al. 0) and EDWARDS et al. (2) made clear that two sets of fundamental parameters are useful in describing vapor-liquid equilibria of volatile weak electrolytes, (1) the dissociation constant(s) K of acids, bases and water, and (2) the Henry s constants H of undissociated volatile molecules. A thermodynamic model can be built incorporating the definitions of these parameters and appropriate equations for mass balance and electric neutrality. It is complete if deviations to ideality are taken into account. The basic framework developped by EDWARDS, NEWMAN and PRAUSNITZ (2) (table 1) was used by authors who worked on volatile electrolyte systems the difference among their models are in the choice of parameters and in the representation of deviations to ideality. 

The QET is not the only theory in the field indeed, several apparently competitive statistical theories to describe the rate constant of a unimolecular reaction have been formulated. [10,14] Unfortunately, none of these theories has been able to quantitatively describe all reactions of a given ion. Nonetheless, QET is well established and even the simplified form allows sufficient insight into the behavior of isolated ions. Thus, we start out the chapter from the basic assumptions of QET. Following this trail will lead us from the neutral molecule to ions, and over transition states and reaction rates to fragmentation products and thus, through the basic concepts and definitions of gas phase ion chemistry. 

Although there is no controversy about the basic definition of stability constants, physical chemists and biochemists handle the concepts involved and the resulting calculations differently. Physical chemists think in terms of reactive species and biochemists in terms of total concentrations of components, A further source of confusion is the differing definitions of apparent constant. To a physical chemist the stability constant for MgATP formation... 

A similar system, (CH3)2C=CH X, was studied by Endrysova and Kraus (55) in the gas phase in order to eliminate the possible leveling influence of a solvent. The rate data were separated in the contribution of the rate constant and of the adsorption coefficient, but both parameters showed no influence of the X substituents (series 61). A definitive answer to the problem has been published by Kieboom and van Bekum (59), who measured the hydrogenation rate of substituted 2-phenyl-3-methyl-2-butenes and substituted 3,4-dihydro-1,2-dimethylnaphtalenes on palladium in basic, neutral, and acidic media (series 62 and 63). These compounds enabled them to correlate the rate data by means of the Hammett equation and thus eliminate the troublesome steric effects. Using a series of substituents with large differences in polarity, they found relatively small electronic effects on both the rate constant and adsorption coefficient. 

The most widely studied physical property of carbanions is their basicity, which of course is a direct measure of the acidity of the parent carbon acid. Carbon acidity measurements date back to the early part of the twentieth century and a myriad of techniques have been employed for the measurements. Although early measurements were only able to provide semiquantitative data, more recent ones have resulted in accurate acidity measurements across a vast range of effective acid dissociation constants, Ka values. This section will begin with a brief description of definitions and methodologies followed by representative data as well as applications of those data. 

Berthollet s theory actually challenged Proust s basic rule of definite proportion, which was the cause of the debate, but the empirical evidence of both sides was inadequate to resolve the dispute. The controversy was more important by what it suggested than by what it accomplished. Henceforth, it became imperative to seek a clear understanding of the causes underlying the apparent fact of constant proportions. ... 

J- for Hydroxide Solutions in Aqueous Ethanol. From the pK2(H20) values and values of log CArCH(OH)cr/CArCHO a a given Coh- in a given solvent mixture, it is possible to calculate J- values for the solvent mixture under consideration using Equation 1 where pKw is the autoprotolytic constant of water and pK2(H20) is inserted for pK2- This definition expresses J values with reference to a standard state in pure water, and therefore basicities of sodium hydroxide solutions in mixed solvents can be compared to basicities of sodium hydroxide solutions in water by J values. 

Table I presents six basic equations in a general way. Those on the left apply to transfer within a phase A, and those on the right to transfer across a phase boundary AB. The top row expresses the mutual definition of force F, proportionality constant K, and potential . The second row expresses the phenomenological proportionality between flux J and force F. The bottom row states the conservation constraints. The left equation says merely that in a given volume the difference between the accumulation rate and the emanation rate must be attributed to a source S. As stated, these equations apply to any conserved quantity which is diffusing, either within a phase under the influence of a potential gradient or across a phase under the influence of a potential difference.

In a definitive series of experimental investigations H. N. Wilson showed that the quinolinium salt, (C isNJ fPCV I2M0O3]3- was anhydrous, contained exactly 12 moles of molybdenum trioxide per mole of phosphate, that the precipitate had a negligible solubility and could be dried to constant weight in two hours at 105 °C. This precipitate also lent itself to a precise alkalimetric titration. In the presence of citric acid interference by silica was inhibited so that the method was admirably suitable for the analysis of basic slags or fertilizers.34... 

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