Acidity, pKa values

In this chapter it is clearly impossible to do more than sample the extensive literature on the carbon acidity of sulfinyl and sulfonyl compounds, as it illuminates the electronic effects of these groups, particularly in connection with linear free-energy relationships. There are three main areas to cover first, as already indicated, equilibrium acidities (pKa values) second, the kinetics of ionization, usually studied through hydrogen isotopic exchange and finally, the kinetics of other reactions proceeding via carbanionic intermediates. 

Basicities 565-567 Basis orbitals 2-5 Benzisothiazolinone dioxides 163 Benzofurans 638 Benzoic acids, pKa values of 586 Benzoxathiazine 2-oxides 71 Benzyne intermediates 306 Beta scales 559... 

The bottom portion of Table 8.1 consists of very weak acids11 (pKa above 17). In most of these acids, the proton is lost from a carbon atom, and such acids are known as carbon acids, pKa values for such weak acids are often difficult to measure and are known only approximately. The methods used to determine the relative positions of these acids are discussed in Chapter 5.12 The acidity of carbon acids is proportional to the stability of the carbanions that are their conjugate bases (see p. 175). 

Cacodylic acid, pKa value of 99 Cadherin(s) 187,407 domains 408s Cadmium 317... 

Dicyanocobalamin 870 3,6-Dideoxyhexoses, formation of 747 Dielectric constant 47 Diesenhofer, Johan 84 Diethanolamine, pKa value of 99 Diethylmalonic acid, pKa value of 99 Diethylpyrocarbonate reaction with histidine 126... 

They showed that, in fact, uridine possesses two acidic dissociations, and on this basis would have had to conclude that the sugar moiety was affixed to position 6 (At this time, the 5, 6 -bi8(phenylhydrazino)uridine107 had already been prepared, which excluded position 6. ) A re-examination109(b) of the titrimetric measurements revealed that (a) uracil possesses only one acidic dissociation (pKa 9.42), (b) the higher acidic pKa value for uridine (12.52) is due to dissociation of the sugar moiety rather than being that of the pyrimidine, and (c) 1- and 3-methyluracil possess only one dissociation constant each. Therefore, they concluded that the dissociation constants of uridine and uracil did not contradict the theory of the union at position... 

Rifampin is an amphoteric drug substance theoretical concentration ratio was based on its behavior as an organic acid. pKa value given for aminoglycosides is unconfirmed. 

The proton-dissociation reaction of alkylated ANIs in the excited 5) state tends to decrease significantly in A-monoalkylanilines but to increase in the A-dialkylated derivatives, with much larger activation energies111. The differences in the observed kiiss rate coefficient between protonated aniline and protonated alkylated derivatives has been explained on the basis of the charge density on the N-atom in the excited S state, the water structure in the vicinity of the amino group which acts as a proton acceptor and steric hindrance of the alkyl groups. As a consequence, the acidity (pKa values) and fluorescence lifetime of protonated anilines in aqueous solution are remarkably dependent on the substituent position in the ring. 

The thermodynamic data for complexation of trivalent lanthanide and actinide cations with halate and haloacetate anions are reported. These data are analyzed for estimates of the relative amounts of inner (contact) and outer (solvent separated) sphere complexation. The halate data reflected increasing inner sphere character as the halic acid pKa increased. Use of a Born-type equation with the haloacetic acid pKa values allowed estimation of the effective charge of the carboxylate group. These values were, in turn, used to calculate the inner sphere stability constants with the M(III) ions. This analysis indicates increasing the inner sphere complexation with increasing pKa but relatively constant outer sphere complexation. 

The half-wave potentials ( 1/2) for 4-unsubstituted-, 4-methyl-, 4-phenyl-, 4,l -pyrrolidinyl-, and 4,4 -pyridyl-2-chloroquinazolines and for 2-unsub-stituted-, 2-methyl-, 2-phenyl-, 2,l -pyrrolidinyl-, and 2,4 -pyridyl-4-chloro-quinazolines were measured in dimethylformamide. The values for the latter series gave a satisfactory correlation with the acidic pKa values of 2-unsubsti-tuted-, 2-methyl-, 2-phenyl-, 2,l -pyrrolidinyl-, and 2,4 -pyridyl-quinazolin-4(3H)-ones measured spectrophotometrically in aqueous solution.69... 

Acetic acid, pKa values, 19 Acetonitrile, pKa values, 19 4-aminobenzoic acid, 24 Artificial neural network (ANN) estimation methods, pKa values, 14, 24, 26 Atmospheric CO2, exclusion of, 22-23... 

The order of basicity is the reverse of the order of the acidity of the conjugate acids (pKa values shown below the structures). 

Guthrie JP (1978) Hydrolysis of esters of oxy acids pKa values for strong acids Bronsted relationship for attack of water at methyl fi ee energies of hydrolysis of esters of oxyacids and a linear relationship between free energy of hydrolysis and pKa holding over a range of 20 pK units. Can J Chem 56 2342-2354... 

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