Acid-base equilibria measuring

A study of some C—H acids in dimethyl sulfoxide solution led to an acidity order that almost paralleled that found in the gas phase, whereas in protic solvents the order was different [116, 124, 125]. This result highlights the importance of specific solute/solvent interactions such as hydrogen bonding in comparing acid/base equilibria measured in the gas phase and in solution. 

One can write acid-base equilibrium constants for the species in the inner compact layer and ion pair association constants for the outer compact layer. In these constants, the concentration or activity of an ion is related to that in the bulk by a term e p(-erp/kT), where yp is the potential appropriate to the layer [25]. The charge density in both layers is given by the algebraic sum of the ions present per unit area, which is related to the number of ions removed from solution by, for example, a pH titration. If the capacity of the layers can be estimated, one has a relationship between the charge density and potential and thence to the experimentally measurable zeta potential [26]. 

Does this model give us a practical solution for the synthesis of monosubstitution products in high yields The model teaches us that reactions are not disguised by micromixing if the intrinsic rate constant (in Scheme 12-84 k2o and k2v>) is significantly less than 1 m-1s-1. As discussed in Section 12.7, the intrinsic rate constant refers to unit concentrations of the acid-base equilibrium species involved in the substitution proper, not to analytical concentrations. Therefore, if the azo coupling reaction mentioned above is not carried out within the range of maximal measured rates (i.e., with the equilibria not on the side of the 1-naphthoxide ion and... 

Reactions in most functional micelles involve nucleophilic attack by an anionic moiety, e.g. oximate, hydroxamate, thiolate or alkoxide. Therefore it may be necessary to take into account the acid-base equilibrium which generates the anionic moiety. The simplest approach is to work at a pH such that deprotonation is essentially quantitative, but if this cannot be done the extent of deprotonation has to be measured directly or estimated. 

It is also possible to create a redundancy between measurements with models linking several variables. Static and robust models like acid-base equilibrium and gas-liquid equilibrium can be used easily. However, models with strong assumptions and/or with unknown validity should be used with caution. In this last case, we also have to take into account that the model itself can be faulty and a dimension of the state-universe of the corresponding bba is the faulty state of the model. 

With reference to a solvent, this term is usually restricted to Brpnsted acids. If the solvent is water, the pH value of the solution is a good measure of the proton-donating ability of the solvent, provided that the concentration of the solute is not too high. For concentrated solutions or for mixtures of solvents, the acidity of the solvent is best indicated by use of an acidity function. See Degree of Dissociation Henderson-Hasselbalch Equation Acid-Base Equilibrium Constants Bronsted Theory Lewis Acid Acidity Function Leveling Effect... 

NMR spectroscopy, which was developed in the late 1950s as a most powerful tool for structural analysis of organic compounds, has also proven to be useful for acidity determinations. The measurement of the ionization ratio has been achieved by a variety of methods demonstrating the versatility of this technique. If we consider the general acid-base equilibrium Eq. (1.26) obtained when the indicator B is dissolved in the strong acid HA, then Up, and fcd, respectively, are the rates of protonation and deprotonation. 

Indirect Exchange Rates. In this case, the line shape is indirectly related to the acid-base equilibrium. Besides measuring intermolecular processes like the proton exchange rates, DNMR often has been used to measure intramolecular processes like conformational changes that occur on the same time scale. When the activation energy of such a process is very different in the acidic and basic forms for an indicator, DNMR can be used to measure the ionization ratio. 

Since solid acid catalysts are used extensively in chemical industry, particularly in the petroleum field, a reliable method for measuring the acidity of solids would be extremely useful. The main difficulty to start with is that the activity coefficients for solid species are unknown and thus no thermodynamic acidity function can be properly defined. On the other hand, because the solid by definition is heterogeneous, acidic and basic sites can coexist with variable strength. The surface area available for colorimetric determinations may have widely different acidic properties from the bulk material this is especially true for well-structured solids like zeolites. It is also not possible to establish a true acid-base equilibrium. 

The plot of the pH-dependence (Fig. 18) indicates qualitatively a participation of an intermediate acid-base equilibrium. Evaluation of rate constants kr and kg is made difficult by the inaccessibility of the dissociation constant of reaction (24 b) which corresponds to protonation of a radical anion. ESR would be a suitable method for the determination of the dissociation constants of at least the more stable radical anions. Another possibility for obtaining at least an approximate value of the equilibrium constant is the measurement of the shifts of the half-wave potentials of the more negative wave at potential 3 with pH. Because the half-wave potential of this wave is known to be sensitive to the... 

Acid solutions are often analyzed by titration with a solution of a strong base of known concentration similarly, solutions of bases are analyzed by titration with a strong acid. In either case, the measured pH is plotted as a function of the titrant volume. Calculation of a pH titration curve is a particularly good introduction to acid-base equilibrium calculations since a variety of calculations are involved. 

In the case of the gel, on the other hand, the back titration with an acid for the sample dispersion, which has already been titrated with a base until an equivalent point, should be possible, since precipitation does not need to be taken into consideration. In contrast to the polymer, however, there are several difficulties in the analysis of the titration data for example, how to estimate the real acid-base equilibrium within the gel phase from the pH measurements of the outer solution (see Sec. IV.C.2). So far, no study has dealt with the potentiometric titrations of polyelectrolyte gels. We neverthe-... 

It is convenient to discuss the cobalt-substituted carbonic anhydrase enzyme, since its electronic spectra are markedly pH-dependent and easy to measure (Figures 2.7 and 2.8). The spectra are well-shaped, and a sharp absorption at 640 nm is present at high pH and absent at low pH. Whereas CoHCA I is almost entirely in the low-pH form at pH 5.7, this is not true for the CoBCA II isoenzyme. The acid-base equilibrium for Co-substituted carbonic anhydrase (deprotonation of the metal-coordinated water) involves three species ... 

All nucleophiles are bases (1). In fact, within the definition of Lewis (2), nucleophilicity is basicity. Following Ingold (3), however, physical-organic chemists have normally used the Brpnsted-Lowry definition (4, 5) of bases as affinity for protons. Likewise, nucleophilicity referred to affinity for nuclei of other elements, most often carbon (3). Another classification reserves basicity, and its counterpart acidity, for equilibrium measurements, while nucleophilicity and its counterpart electrophilicity refer to rate measurements (6). The terms carbon basicity and hydrogen nucleophilicity have been employed (7-9). This classification does not seem to have gained much acceptance. 

Binding constants are a special case of equilibrium constants such as acid-base equilibrium constants (best known as pATa and pAfb) and solubility equilibrium constants (Ks). Binding constants measure the bonding affinity between two or more molecules at equilibrium. In supramolecular chemistry, binding constants for host-guest complexation or host-host aggregation (e.g., dimerization) are usually... 

Any quantitative measure of the acidity of organic acids or bases involves measuring the equilibrium concentrations of the various components in an acid-base equilibrium. The strength of an acid is then expressed by an equilibrium constant. The dissociation (ionization) of acetic acid in water is given by the following equation ... 

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