Minimal kinetic mechanism and general equation for deuterium isotope effects on enzymic reactions: uncertainty of detecting a rate-limiting step

Biochemistry ◽  
1981 ◽  
Vol 20 (14) ◽  
pp. 4056-4061 ◽  
Author(s):  
Dexter B. Northrop
Keyword(s):  
General Equation ◽  
Isotope Effects ◽  
Kinetic Mechanism ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Deuterium Isotope Effects ◽  
Rate Limiting

The Meyer Reaction of Phenylnitromethane in Acid. III. The Tautomerization to the aci-Form

1971 ◽  
Vol 49 (21) ◽  
pp. 3493-3501 ◽  
Author(s):  
J. T. Edward ◽  
P. H. Tremaine
Keyword(s):  
Rate Increase ◽  
Isotope Effects ◽  
Dilute Acid ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Acid Catalyzed ◽  
Deuterium Isotope Effects ◽  
Rate Limiting ◽  
Hydrolysis Of ◽  
Competing Reactions

The rate-acidity profiles for the Meyer rearrangement–hydrolysis of phenylnitromethane in sulfuric, perchloric, and hydrochloric acid show a maximum near 3 M acid. Ring-substituted phenylnitromethanes also show a maximum in their rate profiles, at slightly different acid concentrations. These maxima arise because the slow formation of the aci-form is followed by two competing reactions: fast tautomerization back to the nitro-form, and fast rearrangement–hydrolysis to the Meyer products. The rearrangement is rate-limiting in dilute acid and is acid-catalyzed, causing the rate increase. In more concentrated acid, the rate-limiting step is the nitro to aci tautomerization, which is not acid-catalyzed, and which goes more slowly as the activity of water decreases.The tautomerization was studied by means of primary and solvent deuterium isotope effects, and was found to occur through proton abstraction by water, through a transition state closely resembling the products.

scholarly journals Comment on “Topography of the free energy landscape of Claisen–Schmidt condensation: solvent and temperature effects on the rate-controlling step” by N. D. Coutinho, H. G. Machado, V. H. Carvalho-Silva and W. A. da Silva, Phys. Chem. Chem. Phys., 2021, 23, 6738

2021 ◽  
Vol 23 (38) ◽  
pp. 22199-22201
Author(s):  
Charles L. Perrin
Keyword(s):  
Temperature Effects ◽  
Isotope Effects ◽  
Energy Landscape ◽  
Kinetic Isotope Effects ◽  
Chem Phys ◽  
Kinetic Isotope ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Rate Controlling Step

The referenced article in PCCP presents calculations of solvent kinetic isotope effects that indicate that the rate-limiting step in base-catalyzed chalcone formation in aqueous solution becomes the second enolization.

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