Ionization constant characterization

Separate ionization constants designated Ki and K2 respectively characterize the two successive ionization steps of a dicarboxylic acid... 

This constant characterizes the ionization of a particular substituted benzoic acid in water at 25 °C relative to that of benzoic acid itself. This definition reduces equation 7.4.22 to... 

The tautomeric ratios characterizing the whole complex scheme of uracil cannot be evaluated. Only the tautomeric equilibrium constant Kt32,28 for uracil was calculated by Katritzky and Waring.97 The ionization constants determined by two different methods (see Table XVII) give the values of 104° and 103 3 for X,32,28 of 1-methyluracil. 

Experiments similar to those described in Fig. 1, and titrations of Aryl2CH + MCl,T+]/MCl mixtures with NR4+C1 solutions have been performed to characterize the relative chloride affinities of other Lewis acids MCI, [40], It turned out, however, that the well-defined behavior of BCI3 could not be observed with other systems. The positions of all other metal chlorides in Scheme 7, therefore, have only qualitative character. Relatively small concentrations of SbCl5 and GaCl3 were sufficient to completely ionize (p-CICeHUhCHCl, the weakest chloride donor of this series. The values of these ionization constants could not be deter-... 

In the early stage of preformulation, characterization of the drug molecule involves ionization constants and partition coefficient determinations, aqueous and nonaqueous kinetic and equilibrium solubility determination, pH solubility profile, chemical stability assessment, and salt and polymorph screening. Assessment of biopharmaceutics and toxicological screening are also essential... 

An a priori prediction for cocrystal formation has been reported that is based on intermolecular pair interactions that have been characterized using pulsed gradient spin-echo nuclear magnetic resonance, and tested against the conventional ionization constant guideline for 25 molecular pairs [17]. This approach was shown to work well even in different... 

Quinoxalines are weakly basic the basicities of quinoxaline derivatives were determined potentiometrically and of 5,6-substituted 2,3-dimethylquinoxalines either spectrophotometri-cally, or by potentiometric titration. Quinoxaline has a melting point of 29-30 C, a boiling point of 108-111 °C/12 Torr, and 0.56 (— 5.52) quinoxaline 1-oxide has a pK of 0.25 and is, therefore, a weaker base than the parent compound.Ionization properties (e.g., ionization constants) show that quinoxaline is a relatively weak base. Quinoxaline has a dipole moment of 0.51 D in benzene." Polarographic studies were performed on quinoxalines," and electrochemical and spectroscopic characterization of, V,A -dialkylquinoxalinium salts has been reported. ... 

A strong acid is a substance that reacts completely with water, so that the acid ionization constant defined in Eq. (10) or (11) is effectively infinite. This situation can only be achieved if the conjugate base of the strong acid is very weak. A weak acid will be characterized by an acid ionization constant that is considerably less than unity, so that the position of equilibrium in the reaction represented in Eq. (8) favors the existence of unreacted free acid. 

Because aqueous solutions of anions are commonly prepared by the dissolution of a salt containing that anion, reactions of the type described by Eq. (16) are often termed hydrolysis reactions. Eq. (16) is necessarily characterized by its base ionization constant expression ... 

Since the protonated base can be considered as an acid corresponding to the free base, it is possible to characterize both, acids and bases with the same parameter, i.e. the acid ionization constant. The or the pJiTa respectively, is the key parameter indicating the strength of an electrolyte (Table 35.1). 

Spinaceamines are fairly strong bases with two basic centres. The highest protonation constants correspond to the N-5 atom of SpA (8.90) and the N-5 atom of SpN (8.66), while the smaller constants characterize the basicity of the imidazole ring in the monocation of SpA (4.89) and SpN (4.96). The acid ionization constant of SpN (pKg) is 1.65 and is comparable with the pK of histidine (1.96) (73JCS(D)323). SpNs 517, 519, 563 and 564 substituted at an N-atom easily take up methyl halides to afford monoquaternary salts 559-562 at the N-5 atom. More stringent conditions are required to obtain diquaternary salts 565 (82MI5). 

The time-averaged potential profile is shown in Figure 4b. As ions cannot follow the oscillations in the applied electric field, it is this profile that ions experience. The bulk plasma is characterized by a constant potential, Vpi. In both sheaths (regions between plasma bulk and the electrodes), the ions experience a potential difference and are accelerated towards the electrodes. This leads to energetic ion bombardment of the electrodes. Electrons are expelled from the sheaths, so all ionization and dissociation processes must occur in the plasma bulk. Plasma light, resulting from emission from excited molecules, is emitted only from the plasma bulk the sheaths are dark. 

The probability of charging a trap when a metal particle is ionized by a metastable atom can be characterized by the ratio of the time the barrier stays in nonequilibrium state to the time constant of trap recharging. 

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