PKa , Table values

The line-broadening data as a function of pH, typically shown for the W(IV) in Figs. 13 and 14, incorporating the known pKa values (Table II), were fitted in 5 X 5 Kubo-Sack matrices describing the exchange based on the above schemes (6, 57). The experimentally determined chemical shift and linewidth data in the absence of exchange for the aqua oxo, hydroxo oxo, and dioxo species and the pH-dependent species distribution as calculated from the acid dissociation constants for the four systems were all introduced in the different matrices and the spectra were computer simulated. For each set of chosen rate con-... 

The dioxo complexes of W(IV) and Mo(IV), having high pKa values (Table II), are formed via hydrolysis as the rate-determining step (Scheme 4) and the observed rate constants for the inversion along the O-M-O axis for the W(IV) and the Mo(IV) complexes are therefore defined by Eq. (18). These were calculated as a function of pH, using the proton exchange rate constants (Table IV) and the acid dissociation constants (Table II)... 

The Bronsted correlation for five-membered rings shows that effects of structure on reactivity and on acidity are related. Variations in rate constants for quaternization and in pKa values (Table III) are understandable in terms of resonance and inductive effects of the heteroatom X.120 The effects on the energy of a transition state leading to quaternized product are similar but smaller than those on the energy of protonated material. The following considers in more detail the influence of benzo-fusion. 

The elution profile shown in Fig. 3-4 indicates that glycine, alanine, valine, and leucine can be separated clearly by ion-exchange chromatography yet these four amino acids have almost indistinguishable sets of pKa values (Table 3.2). How can you account for this behavior ... 

Table 2. Predicted intrinsic and apparent pKa values for the Cys403 residue in Yersinia phosphatase for different models of the structure the data refer to a temperature of 293 K and an ionic strength corresponding to 150 mM of monovalent salt. See the text for the detailed description of the conditions under which each pK estimation was made. The experimentally determined value is 4.67 [39]...

Base is chosen so as to favor enolate formation. Acidity of C-H bond must be greater (lower pKa value) than that of the conjugate acid of the base (C S table 1.1, pg 3)... 

Table 4 pKa Values of Pyrrole-, Furan-, Thiophene-, Selenophene- and Tellurophene-earboxylie Aeids... 

The pKa values of a number of isoxazoles have been reported and again the weakly basic nature of the ring, being less than oxazole, is demonstrated (see Table 3) (7iPMH(3)i. p. 23). 

There is a discrepancy in the literature concerning 4-hydroxy-cinnoline. Whereas two measurements of pKa values indicate that the cinnolinone structure predominates by a large factor in aqueous solution (see Table III), comparison of the ultraviolet spectra of 4-hy-... 

Many types of carbonyl compounds, including aldehydes, ketones, esters, thioesters, acids, and amides, can be converted into enolate ions by reaction with LDA. Table 22.1 lists the approximate pKa values of different types of carbonyl compounds and shows how these values compare to other acidic substances we ve seen. Note that nitriles, too, are acidic and can be converted into enolate-like anions. 

The structures, abbreviations (both three- and one-letter), and pKa values of the 20 amino acids commonly found in proteins are shown in Table 26.1. All are... 

Interestingly, comparison of the values of pAHB and the acidity constants pKa in a series of the same family of compounds, such as carbonyl compounds, amines, pyridines and sulphoxides, shows that a good correlation exists between p/CHB and pgiving straight lines in each series of compounds with parallel slopes. This enables one to calculate the difference of the several pKa values at the same p/CHB value, and vice versa. Thus, at p= 0, p/CHB values of various functional groups were determined and are shown in Table 13. 

They have also demonstrated that a linear energy relationship exists between pKa values of sulphoxides and the hydrogen bonding ability which was determined by IR-stretching shift of the OH band in PhOH in CC14. Oae and coworkers173 determined the pKa values of diaryl sulphoxides and found that the substituent effect does not correlate with the Hammett o values but approximately with the a values. The pKa values thus obtained are summarized in Table 19. 

TABLE 2. pKa values acids in water at 25 °C of p- and m-sulfonio- and sulfonyl-benzoic ... 

TABLE 4. First pKa values of bis(4-hydroxyphenyl)sul foxides in 50% water-ethanol at 25 °C and related Hammett (r-values (after Reference 33)... 

TABLE 9. pKa values of various compounds in DMSO (after References 40-42)... 

As in Table 10.1, the experimental pKa values have more significant figures than shown here, and the K, values have been calculated from these better data. 

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