Ionization constant, observed

Table 19 3 lists the ionization constants of some substituted benzoic acids The largest effects are observed when strongly electron withdrawing substituents are ortho to the carboxyl group An o nitro substituent for example increases the acidity of benzoic acid 100 fold Substituent effects are small at positions meta and para to the carboxyl group In those cases the values are clustered m the range 3 5-4 5... 

Data are extant in the literature for two other sets of ethynylene compounds. The sets studied are reported in Table XXXIII. Results of correlation are set forth in Table XXXIV and values of Pr in Table XXXV. The ionization constants of 3-substituted propiolic acids, which were first correlated with the Hammett equation by Charton (18), gave an excellent correlation with eq. (2) (set 22-27-1). The results are very much improved by the elimination of the value for X = H (set 33-27-2). The composition of the electrical effect corresponds approximately to that of the Op constants. The magnitude of the electrical effect is significantly less than that observed for the rrans-3-substituted acrylic acids. 

The dissociation constants of brinzolamide were determined by potentiometric titration of the hydrochloride salt with 0.05N NaOH, with two ionizations being observed. The first pKa, attributed to the deprotonation of secondary ammonium moiety, was observed at 5.8 8. The second pKa, attributed to deprotonation of the sulfonamide group, was at 8.48. 

Sulfur dioxide dissolves in water, forming a weak acid solution of sulfiirous acid, H2S03 however, the pure substance H2S03 has never been isolated. At 101.3 kPa (1 atm) sulfur dioxide pressure, the solubility of sulfur dioxide is 18.5% at 0°C and 5.1% at 40°C. Lower solubilities are observed when other diluent gases, eg, air, are present. At 25°C, the hypothetical H2S03 has a first ionization constant of 1.72 x 10-2 and a second ionization constant of 1.1 x 10-9. Atlow temperatures, concentrated sulfurous acid affords a crystalline hydrate, S02 6H20 [24402-69-5]. 

In CT complexes such as that between furan and tetracyanoethylene split maxima are often observed in the electronic absorption spectrum, since inner, as well as the outermost, occupied orbitals of the (donor) heterocycle are involved. However, the absorption maxima run parallel with the first ionization constants and can be used to predict them (75JCS(F1)2045, 68MI31000). Again, furan is thought to quench the fluorescence of 1-cyanonaphthalene because it forms an exciplex intermediate with a fluorescence of its own to the red side of the original one the exciplex has CT character and the frequency of the new fluorescence correlates with the first ionization potentials in a series of furans (75CC203). 

Nelson et al.7I have defined a pyridine AT-oxide substituent constant, difference between the ionization constants of pyNOH+ and substituted pyNOH+ acids. The value of 2.09 has been chosen to give approximate numerical comparability with other sets of substituent constants in common use. Fairly consistent correlations between experimental parameters related to donor strength have been observed, e.g. the reduction of v(V=0) in [VO(acac)2] when 4-substituted pyNO ligands are added. 

The pH-dependent fluorescence of 1,6-naphthalenediol (ND) (29), INpOH, and 2NpOH has been studies in the presence of a-CD and (3-CD [168], Inclusion complexation of ND inside the CD cavity greatly reduced proton transfer in pho-toexcited ND. This led to the interesting observation of four pH-dependent bands, attributed to four different forms of ND molecular (29), (3-ionic (30), a-ionic (31), and diionic (32), having fluorescence maxima at 365, 400, 470, and 440 nm, respectively. Ground-and excited-state ionization constants of 2NpOH in inclusion... 

Ionization constants. Known pKt values for pyrazine and six methylated derivatives showed good correlation with newly calculated electron densities on the nitrogen atoms 1052 such a correlation was also observed for 1,4-di-methylpiperazine and a series of (distantly) related m- and p-bis(dimethy-laminomethyl)benzene derivatives.1039... 

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-... 

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