Bronsted correlation extended

In view of the substantial use of the extended Bronsted correlation it is always the convention to name the Bronsted exponent as P with a subscript to indicate which reaction is being measured and to distinguish it from the parameters of the standard acid-base correlations. 

The extended Bronsted correlation for the aminolysis of the 2,4,6-trinitrophenyl ester is linear with an equation ... 

Figure 4 Extended Bronsted correlations. The lines are theoretical...

Figure 15 Extended Bronsted correlation exhibits relatively substantial microscopic medium effects...

Together with other workers in the field Jencks [10] has extended the Bronsted correlation to include a meaning for the exponents provided one is prepared to work within a given framework of assumptions. A model for the equihbrium between acyl esters and their hydrolysis products (Eqn. 16) might be the ionisation of the phenol where the charge on phenol and phenolate oxygen is defined as zero and — 1 respectively. 

Since spillover phenomena have been most directly sensed through the use of IR in OH-OD exchange [10] (in addition, in the case of reactions of solids, to phase modification), we used this technique to correlate with the catalytic results. One of the expected results of the action of Hjp is the enhancement of the number of Bronsted sites. FTIR analysis of adsorbed pyridine was then used to determine the relative amounts of the various kinds of acidic sites present. Isotopic exchange (OH-OD) experiments, followed by FTIR measurements, were used to obtain direct evidence of the spillover phenomena. This technique has already been successfully used for this purpose in other systems like Pt mixed or supported on silica, alumina or zeolites [10]. Conner et al. [11] and Roland et al. [12], employed FTIR to follow the deuterium spillover in systems where the source and the acceptor of Hjp were physically distinct phases, separated by a distance of several millimeters. In both cases, a gradient of deuterium concentration as a function of the distance to the source was observed and the zone where deuterium was detected extended with time. If spillover phenomena had not been involved, a gradientless exchange should have been observed. 

The [Co(NH3)sOH]2+-promoted hydrolysis (and that promoted by other exchange-labile anc non-labile metal hydroxide species) of 2,4-dinitrophenyI acetate and 4-nitrophenyl acetate hat been studied in some detail.19 Kinetic studies (25 °C, / = 1.0 M) show that these reactions follov shallow Bronsted slopes (/ = 0.33 and 0.40) for the two substrates which extend over a range o 1010 in nucleophile basicity. A correlation is reported which allows the prediction of reactioi... 

Streitwieser and co-workers have extended their measurements of equilibrium acidities in cyclohexylamine to determination of exchange rates.69 They have made quantitative correlations between exchange rate and the pKa s determined by equilibrium methods for various aromatic compounds and have thus been able to verify that the Bronsted relation holds for these substances and to find Bronsted coefficients a for various types of compounds. A third method for evaluating p/Ca of weak acids, which has been used by Applequist70 and by Dessy,71 involves the study of exchange reactions of organometallic compounds (Equations 3.54 and 3.55). 

FIGURE 6. Extended Bronsted plot of ogkH+ vs pK%H for the protonation of some highly activated alkenes RC(X)=CH2, R = H, CH3, Ph see equations 55 and 56 in text, as well as Table 16. The squares represent alkenes with / -substituents these were not included in the correlation... 

The slope of the Swain-Scott correlation, s = 0.26, indicates that the reaction is about one quarter as sensitive to change in the nucleophile as is the standard reaction with methyl halides (where 5=1.0). This result is consistent with the small value of (0.4) for the extended Bronsted slope for reaction of the substrate with primary aliphatic amines and a... 

Using a Bronsted equation in which the ionic strength term has been derived from an extended Debye-Huckel correlation, it has been shown that for the ions M+ = Li+, Na+, K+, Rb+, or Cs+ the first (Ati) pathway is operative but only in the case of Li+ to an appreciable extent. For the cations Li+ or Na+, the Arg route is operative whereas for K+, Rb+, or Cs+ the reaction proceeds via the kt mechanism, the rate constants extrapolated to zero ionic strength being remarkably similar. 

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