Kinetic acidity of carbon acids: initial and transition state enthalpies of transfer from water to aqueous dimethyl sulphoxide in the hydroxide ion catalysed ionization of acetophenone

1990 ◽  
pp. 1081-1083 ◽  
Author(s):  
Markku Lahti ◽  
Alpo Kankaanperä ◽  
Helmi Säpyskä
Keyword(s):  
Transition State ◽  
Dimethyl Sulphoxide ◽  
Hydroxide Ion ◽  
Enthalpies Of Transfer ◽  
Kinetic Acidity ◽  
Carbon Acids

Transition state enthalpies of transfer in aqueous dimethyl sulfoxide solutions. The hydroxide catalyzed ionization of chloroform

1977 ◽  
Vol 55 (1) ◽  
pp. 99-101 ◽  
Author(s):  
John R. Jones ◽  
Richard Fuchs
Keyword(s):  
Transition State ◽  
Dimethyl Sulfoxide ◽  
Enthalpies Of Solution ◽  
Hydroxide Ion ◽  
Enthalpies Of Transfer ◽  
Aqueous Dmso

The accelerating effect of added dimethyl sulfoxide on the rate of hydroxide-catalyzed ionization of chloroform in water has been examined in terms of the solvation of reactants and transition state. Enthalpies of solution of chloroform in water, DMSO, and mixtures of the two have been measured. From these, together with enthalpies of activation for the detritiation of chloroform, and enthalpies of transfer of hydroxide ion from water to aqueous DMSO mixtures, transition state enthalpies of transfer have been calculated. The reaction is accelerated by small concentrations of DMSO because of increased transition state solvation, but by large DMSO concentrations due to reduced solvation of hydroxide ion. Transition state solvation is unlike that of the reactants, but resembles that expected for CCl3− ion.

Transition State Imbalance in the Deprotonation of Substituted 2-Tetralones by Hydroxide Ion

1997 ◽  
Vol 119 (52) ◽  
pp. 12722-12726 ◽  
Author(s):  
John B. Nevy ◽  
David C. Hawkinson ◽  
Grzegorz Blotny ◽  
Xudong Yao ◽  
Ralph M. Pollack
Keyword(s):  
Transition State ◽  
Hydroxide Ion

Rate and equilibrium studies of the deprotonation of benzylic ketones bearing pyridinium cations

1989 ◽  
Vol 67 (3) ◽  
pp. 428-432 ◽  
Author(s):  
John W. Bunting ◽  
Dimitrios Stefanidis
Keyword(s):  
Activation Parameters ◽  
Kinetic Studies ◽  
Similar Data ◽  
Equilibrium Studies ◽  
Hydroxide Ion ◽  
Pyridinium Cation ◽  
Carbon Acids ◽  
Entropy Of Activation ◽  
Pyridinium Cations ◽  
Conjugate Base

Rates and equilibria for the deprotonation of four benzylic ketones containing pyridinium substituents (1, 2, 5, and 6) have been investigated in basic aqueous solution (ionic strength 0.1) over the range 15–45 °C, and thermodynamic and activation parameters have been evaluated. Similar data are also reported for the deprotonation of nitroethane. The kinetic preference for hydroxide ion addition to the carbonyl group in competition with the thermodynamically preferred enolate ion formation, which was previously reported for the 1-methyl-4-phenylacetylpyridinium cation (1) and its 3-phenylacetyl isomer (2), is also found for the 1-(1-methyl-2-oxo-2-phenylethyl)pyridinium cation (6). Rates of equilibration of the 1-(2-oxo-2-phenylethyl)-pyridinium cation (5) with its enolate ion conjugate base are too rapid to allow investigation by stopped-flow spectrophotometry. For the hydroxide ion catalyzed deprotonation of each of 1, 2, 6, and nitroethane, [Formula: see text] is more negative than ΔS0. This difference, which represents the entropy of activation for protonation of the conjugate base of each of these carbon acids by water, is approximately constant at [Formula: see text] = −4.9 ± 0.5 cal deg−1 mol−1. Keywords: carbon acids, kinetic studies, deprotonation, activation parameters, pKa values.

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