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Acid ionization isotope effects

The basicities of some phosphinamides (84) have been measured and the acid-catalysed hydrolysis studied. Unsubstituted and A -alkyl derivatives follow an A2 mechanism of reversible protonation followed by ratedetermining water attack. However, the rates for the A -aryl derivatives follow Hq (but with a slope of 0.5), and an A mechanism was suggested as most consistent with this fact and the solvent isotope effect. The anomalous dependence on Ho, together with the large negative value of A5, while not necessarily excluding an ionization mechanism, leaves the question in some doubt. [Pg.114]

A study of acid-catalysed enolization and carbon-acid ionization of isobutyrophenone has combined the solvent isotope effect k /kv = 0.56 and substrate isotope effect kH/kD = 6.2 determined for the enolization in H2O and D2O with literature information in order to estimate the solvent isotope effect on the enolization equilibrium, A e(H20)/A e(D20) = 0.92, and on the CH ionization of butyrophenone, kf (R20)/kK(D20) = 5.4.130 This is the first report of an isotope effect on AY forketo-enol equilibrium of a simple aldehyde or ketone. [Pg.345]

Kresge, A. J., and Chiang, Y. Solvent isotope effects on the ionization of hydrofluoric acid. J. Phys. Chem. 77, 822-825 (1973). [Pg.833]

The solvent isotope effect in the decarboxylation of 2,4-dihydroxy-benzoic acid is ( atcoohJhjO /( ArcooD)D,o = 6.25. The solvent isotope effect on the acid ionization constant of 2,4-dihydroxybenzoic acid has been determined separately, by potentiometric methods ... [Pg.76]

A study of acid-catalysed enolization and carbon-acid ionization of isobutyrophenone has combined the solvent isotope effect — 0.56 and substrate isotope effect... [Pg.345]

Chemical studies also support the indicated mechanism. For example, the p-oxoacid intermediate formed in step h of Eq. 13-48 or Fig. 13-12 has been identified as a product released from the enzyme by acid denaturation during steady-state tumover. Isotopic exchange with in the solvent and measurement of C isotope effects have provided additional verification of the mechanism. TTie catalytic activity of the enzyme is determined by ionizable groups with piC values of 7.1 and 8.3 in the ES com-plex. ... [Pg.707]

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See also in sourсe #XX -- [ Pg.359 ]



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Acid ionization

Ionization effective

Ionization effects

Ionization, isotope effect

Ionized acids

Isotopes acids

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