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

Initial state and transition state contributions to solvent effects on activation enthalpies for substitution reactions of tris(1,10-phenanthroline)iron(II) in aqueous methanol

1983 ◽  
Vol 8 (3) ◽  
pp. 148-152 ◽  
Author(s):  
Michael J. Blandamer ◽  
John Burgess ◽  
Timothy Digman ◽  
Philip P. Duce ◽  
John P. McCann ◽  
...  
Keyword(s):  
Transition State ◽  
Solvent Effects ◽  
Aqueous Methanol ◽  
Substitution Reactions ◽  
Initial State

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.

Spectator catalysis in the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by "hydroxypropyl-β-cyclodextrin"

1996 ◽  
Vol 74 (5) ◽  
pp. 745-752 ◽  
Author(s):  
Timothy A. Gadosy ◽  
Oswald S. Tee
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Competitive Inhibition ◽  
Strong Dependence ◽  
Limited Range ◽  
Initial State ◽  
Cleavage Rate ◽  
Apparent Dissociation Constant ◽  
Potential Inhibitor ◽  
Potential Inhibitors

Aliphatic alcohols that form host–guest complexes with "hydroxypropyl-β-cyclodextrin" retard the cleavage of m-nitrophenyl acetate by hydroxypropyl-β-cyclodextrin in basic aqueous solution, due to competitive inhibition. By contrast, these same species do not inhibit the reaction of p-nitrophenyl acetate and p-nitrophenyl hexanoate to the same extent and, in some cases, the addition of alcohols serves to increase the rate of reaction. The observed reaction kinetics require the presence of a process that has one molecule of the "potential inhibitor" in the transition state for ester cleavage. Rate constants, ka, for the reaction of the {ester•hydroxypropyl-β-cyclodextrin} complexes with a series of potential inhibitors show a strong dependence on the ability of the potential inhibitor to bind to the cyclodextrin. On the other hand, rate constants for the kinetically equivalent reaction of the ester with the {cyclodextrin•potential inhibitor} complex show little dependence on the alcohol structure and they vary over a very limited range. The negative logarithms of the apparent dissociation constant of the potential inhibitor from the transition state show a strong dependence on the ability of the potential inhibitor to bind to hydroxypropyl-β-cyclodextrin, indicating that the binding of the potential inhibitor in the initial state and the transition state is similar. It is concluded that the cleavage of p-nitrophenyl acetate and p-nitrophenyl hexanoate by hydroxypropyl-β-cyclodextrin in the presence of 14 potential inhibitors can occur with the ester largely outside of the hydroxypropyl-β-cyclodextrin cavity during the transition state, allowing the cavity to be occupied by a molecule of potential inhibitor. Key words: cyclodextrin, spectator catalysis, esterolysis.

Sign in / Sign up

Export Citation Format

Share Document