Acidity relative series

G-20 Dicarboxylic Acids. These acids have been prepared from cyclohexanone via conversion to cyclohexanone peroxide foUowed by decomposition by ferrous ions in the presence of butadiene (84—87). Okamura Oil Mill (Japan) produces a series of commercial acids based on a modification of this reaction. For example, Okamura s modifications of the reaction results in the foUowing composition of the reaction product C-16 (Linear) 4—9%, C-16 (branched) 2—4%, C-20 (linear) 35—52%, and C-20 (branched) 30—40%. Unsaturated methyl esters are first formed that are hydrogenated and then hydrolyzed to obtain the mixed acids. Relatively pure fractions of C-16 and C-20, both linear and branched, are obtained after... 

A similar system, (CH3)2C=CH X, was studied by Endrysova and Kraus (55) in the gas phase in order to eliminate the possible leveling influence of a solvent. The rate data were separated in the contribution of the rate constant and of the adsorption coefficient, but both parameters showed no influence of the X substituents (series 61). A definitive answer to the problem has been published by Kieboom and van Bekum (59), who measured the hydrogenation rate of substituted 2-phenyl-3-methyl-2-butenes and substituted 3,4-dihydro-1,2-dimethylnaphtalenes on palladium in basic, neutral, and acidic media (series 62 and 63). These compounds enabled them to correlate the rate data by means of the Hammett equation and thus eliminate the troublesome steric effects. Using a series of substituents with large differences in polarity, they found relatively small electronic effects on both the rate constant and adsorption coefficient. 

Three different sets of experimental aqueous-phase pKa s allow us to judge to what extent solvent effects can be ignored and, where they cannot be ignored, assess the performance of the SMS. 4 model in accounting for solvation. The first involves a diverse set of carboxylic acids and the second a diverse series of alcohols and phenols. Calculated acidities (relative to acetic acid in the case of carboxylic acids and relative to ethanol in the case of alcohols and phenols) have been obtained from the Hartree-Fock 6-311+G model. Previous comparisons with gas-phase acidities suggest that this should be as satisfactory as any other model for this purpose (see, for example. Tables 6-18 and A6-50). 6-3IG geometries have been used in place of 6-311+G geometries in order to save computation time. (See... 

On the other hand, the pKa values of a series of substituted nitromethanes [83] (Table 4.11) suggest that, whilst chlorine bonded directly to the carbanion centre increases acidity relative to hydrogen, fluorine decreases acidity and, therefore, decreases the stability of the corresponding carbanion. 

It should be noted that, in general, the S=0 and S—X bonds are shorter and the O S—O angles are smaller in the XS020H series compared to XS02H. The former correlates with the larger atomic charge on the sulphur atom in the sulphonic acids relative to the sulphones. 

In Section X.A the considerable acid-strengthening effect of C=C was shown for the series butanoic acid, 3-butenoic acid, 3-butynoic acid. This effect is revealed even more dramatically by the values (water, 25 °C) in the series propanoic acid, 4.88 propenoic acid, 4.25 propynoic acid, 1.96. (This is Mansfield and Whiting s value, corrected for the effect of ionic strength see Section X.A.). The - R effect of HC=C may be a factor tending to weaken the acidity of HC=C—COOH by stabilizing the undissociated acid relative to the ionized form (cf the -R effect of Ph in benzoic acid), but it is certainly completely swamped by the +7 effect. 

Competitive resonance effects can be found. In general, C-H bonds alpha to ketones are more acidic than when alpha to ester carbonyls, which are more acidic relative to amide carbonyls, all three of which are more acidic than C-H bonds near carboxylates. The resonance stabilization gained by ionization of the C-H bond is increasingly lower in this series because the O, N, or 0 heteroatom on the ester, amide, or carboxylate, respectively, is increasingly involved in resonance with the carbonyl in the acid prior to ionization of the C-H bond. In such cases, we must consider the role of resonance in stabilizing the HA compound as well as A". 

The phenomenon was established firmly by determining the rates of reaction in 68-3 % sulphuric acid and 61-05 % perchloric acid of a series of compounds which, from their behaviour in other reactions, and from predictions made using the additivity principle ( 9.2), might be expected to be very reactive in nitration. The second-order rate coefficients for nitration of these compounds, their rates relative to that of benzene and, where possible, an estimate of their expected relative rates are listed in table 2.6. 

Substitution of penicillins by 6a-methoxy was found to be compatible with an a-acidic side chain in terms of antibacterial activity, but less beneficial when the side chain contained an a-acyl or a-ureido substituent. However, analogues of the ureido penicillin VX-VC-43 (Table 2) containing a 6a-methoxy substituent (10) were found to combine good stabiUty to P-lactamase and relatively high antibacterial activity (37). Following an extensive program to identify other 6a-substituents that would stabilize the acyl and ureido series of penicillins, the 6a-formamido series (11) represented by formidacillin (BRL 36650) (Table 2) was developed (38). 

Adsorption. Many studies have been made of the adsorption of soaps and synthetic surfactants on fibers in an attempt to relate detergency behavior to adsorption effects. Relatively fewer studies have been made of the adsorption of surfactants by soils (57). Plots of the adsorption of sodium soaps by a series of carbon blacks and charcoals show that the fatty acid and the alkaU are adsorbed independently, within limits, although the presence of excess aLkaU reduces the sorption of total fatty acids (58). No straightforward relationship was noted between detergency and adsorption. 

Many organic reactions involve acid concentrations considerably higher than can be accurately measured on the pH scale, which applies to relatively dilute aqueous solutions. It is not difficult to prepare solutions in which the formal proton concentration is 10 M or more, but these formal concentrations are not a suitable measure of the activity of protons in such solutions. For this reason, it has been necessaiy to develop acidity functions to measure the proton-donating strength of concentrated acidic solutions. The activity of the hydrogen ion (solvated proton) can be related to the extent of protonation of a series of bases by the equilibrium expression for the protonation reaction. 

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