Benzoic acid ionization

The Pi sequence for the former is similar to that for the latter (and for the benzoic acid ionizations of Table XXVII), but the pn sequence is not. 

There is little information for fluoro-substituted sulfinyl groups. Values of a and ffp for SOCFj based on benzoic acid ionization are 0.63 and 0.69 respectively , compared with values of about 0.52 and 0.49 for SOMe (Table 3). Thus the electronegative fluorine somewhat enhances the electron-attracting influence of the sulfinyl function and makes the order more definitely sulfur lone pair to engage in 7t(pp) conjugation. Values of and ffp for SOCF3 based on anilinium ion dissociation are 0.76 and 1.05 respectively . An increase of 0.13 as between and [Pg.509]

The electronic demand parameter r), characteristic of a given process, is equal to the ratio of the coefficients R/D and has been shown to depend on the nature of the active site, skeletal group and medium. Contrary to the general view, electronic demand is roughly the same in magnitude for ar (based on benzoic acid ionization) and o f, scales, but is positive for the former and negative for the latter. 

The cr-constants (Jaffe, 1953) are based on benzoic acid ionization data of greatly variable quality (McDaniel and Brown, 1958). In some cases the uncertainty in the pKA values introduces an uncertainty of + 0.1 unit in the Hammett cr-constants. To avoid the inclusion of this doubt in the cr+-constants only the thermodynamically based [Pg.88]

The substituent parameters and are derived from benzoic acid ionization, and the (Tch x values follow from the acidity of 1 (Table 1), and the factors that influence these quantities have already been discussed in Section II.B. 

Benzoic acids ionization (aq), equilibrium Phenols ionization (aq), equilibrium Benzoylation of aromatic amines in benezene, rate... 

About twenty years ago McDaniel and Brown (28) published their noclassic compilation of (j and Op constants based on the ionization constants of the corresponding benzoic acids. Since that time considerable numbers of new determinations of substituted benzoic acid ionization constants have appeared. As ffR constants are readily determined from Equation 80, it seemed worthwhile... 

Now that a scale for substituent effects has been established, we can determine if other reactions respond to substituents the way benzoic acid does. The goal is to use benzoic acid ionization as a reference reaction that creates a negative charge and compare other reactions to it as a means to see if they also create a negative charge, or conversely, a positive charge. Furthermore, we want to determine if different reactions are more or less sensitive to the substituents than are the acidities of benzoic acid derivatives. To do this, we use the Hammett relationships given in Eqs. 8.23 and 8.24 for thermodynamic and kinetic analyses, respectively. To determine p, plot log(fCx/KH) or log(/cx/ H) versus [Pg.447]

Hammett showed that a plot of log Ka for benzoic acid ionization against a plot of log k for ester hydrolysis over many substituents is reasonably linear. All the meta- or para-substituents are exerting a similar effect in each of these quite dissimilar reactions. 

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