Nonequilibrium transition-state solvation and Marcus work terms. Comparison of their contributions to solvent effects on intrinsic rate constants for proton transfers

1989 ◽  
Vol 111 (23) ◽  
pp. 8631-8639 ◽  
Author(s):  
Joseph L. Kurz
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Intrinsic Rate ◽  
Proton Transfers

Kinetics of reactions of para-substituted phenyl isocyanates with amines and alcohols

1991 ◽  
Vol 56 (8) ◽  
pp. 1662-1670 ◽  
Author(s):  
Ivan Danihel ◽  
Falk Barnikol ◽  
Pavol Kristian
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Substituent Effects ◽  
Steric Effects ◽  
Stopped Flow ◽  
Partial Charges ◽  
Hammett Correlation ◽  
One Step ◽  
Kinetics Of

The reaction of para-substituted phenyl isocyanates with amines and alcohols was studied by stopped-flow method. The Hammett correlation obtained showed that the sensitivity of the above mentioned reactions toward substituent effects is the same as that of analogous reactions of phenyl isothiocyanates (ρ ~ 2). The rate constants of these reactions were found to be affected more by steric effects than by solvent effects. An one step multicentre mechanism with partial charges in transition state has been proposed for the title reactions.

Kinetics of Proton Transfer Reactions of Carbon Acids. II. Reaction of Di-(4-nitrophenyl)methane with Alkoxide Bases

1972 ◽  
Vol 50 (1) ◽  
pp. 24-30 ◽  
Author(s):  
A. Jarczewski ◽  
K. T. Leffek
Keyword(s):  
Proton Transfer ◽  
Transition State ◽  
Rate Constants ◽  
Activation Parameters ◽  
Transfer Reactions ◽  
Activation Process ◽  
Proton Transfers ◽  
Proton Transfer Reactions ◽  
Carbon Acids ◽  
Kinetics Of

The second-order rate constants have been measured over a range of temperatures for the proton-transter reactions from di-(4-nitrophenyl)methane to ethoxide, isopropoxide, and t-butoxide ions in solvents consisting of the corresponding alcohols containing 10% toluene by volume. The activation parameters ΔH≠ and ΔS≠ have been calculated and an interpretation of them is given in terms of solvation effects during the activation process. A comparison between the activation parameters for proton transfers and E2 olefin-forming β-elimination reactions is made and discussed with respect to transition state character of the latter reactions.

Initial state and transition state contributions to solvent effects on rate constants for racemisation and dissociation of the [Fe(phen)3]2+ cation in DMSO-water mixtures

1984 ◽  
Vol 9 (9) ◽  
pp. 347-350 ◽  
Author(s):  
Michael J. Blandamer ◽  
John Burgess ◽  
Stephen D. Cope ◽  
Timothy Digman
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Rate Constants ◽  
Initial State

Transient nitronic acid formation in the protonation of the carbanion of 2,2′,4,4′-tetranitrodiphenylmethane in acidic methanol

1987 ◽  
Vol 65 (8) ◽  
pp. 1980-1986 ◽  
Author(s):  
François Terrier ◽  
Jacques Lelièvre ◽  
Alain-Pierre Chatrousse ◽  
Robert Schaal ◽  
Patrick G. Farrell
Keyword(s):  
Carboxylic Acid ◽  
Solvent Effects ◽  
Rate Constants ◽  
Intrinsic Rate ◽  
Low Ph ◽  
The Other ◽  
Acid Formation ◽  
Other Hand ◽  
Protonated Species ◽  
Nitronic Acid

Rates of deprotonation of 2,2′,4,4′-tetranitrodiphenylmethane (1) by a variety of bases B− and of protonation of the resulting carbanion (2) by the conjugated acids BH in methanol have been measured at 20 °C. The Brønsted αBH coefficients for protonation of 2 by phenol and carboxylic acid buffers are equal to 0.58 and 0.43, respectively, as compared with αBH values of 0.59 and 0.52 respectively, for the same reactions in 50% H2O – 50% DMSO. On the other hand, a comparison of the intrinsic rate constants [Formula: see text] (in the Marcus sense) in the two solvents reveals that the effect of going from 50% H2O – 50% DMSO to methanol is to lower [Formula: see text] for the phenol reactions by a factor of 2 but to increase [Formula: see text]for carboxylic acid reactions by a factor of 5. It is shown that the solvent effects on αBH and [Formula: see text] can all be understood in the context of the Principle of Imperfect Synchronisation (PIS) recently proposed by Bernasconi. In addition, a fast equilibrium protonation of the carbanion 2 is found to precede its conversion to 1 at low pH, i.e., pH < 5. The resulting protonated species is suggested to be the nitronic acid 2,H arising from fast protonation of a para NO2 group of 2. The [Formula: see text] value associated with the ionization of 2,H is ∼4.25.

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