CARBON-13 KINETIC ISOTOPE EFFECTS IN BIMOLECULAR REACTIONS

1962 ◽  
Vol 40 (10) ◽  
pp. 2007-2011
Author(s):  
J. B. Stothers ◽  
A. N. Bourns
Keyword(s):  
Isotope Effects ◽  
Benzyl Bromide ◽  
Kinetic Isotope Effects ◽  
Bimolecular Reaction ◽  
Alcohol Solution ◽  
Ionic Character ◽  
Compound I ◽  
Bimolecular Reactions ◽  
Kinetic Isotope ◽  
Methoxide Ion

Carbon-13 kinetic isotope effects have been measured for the bimolecular reaction of 1-phenyl-1-bromoethane (I) and benzyl bromide (II) with alkoxide ion in alcohol solution. Compound I gave an effect, k12/k13, of 1.0032 ± 0.0005 for reaction with ethoxide ion in ethanol, while II gave k12/k13 = 1.0531 ± 0.0004 for reaction with methoxide ion in methanol. These surprisingly different effects are tentatively interpreted in terms of a model for the transition state having varying degrees of ionic character.

Carbon-13 kinetic isotope effects. IV. The effect of temperature on k12/k13 for benzyl halides in bimolecular reactions

1968 ◽  
Vol 46 (11) ◽  
pp. 1825-1829 ◽  
Author(s):  
Jan Bron ◽  
J. B. Stothers
Keyword(s):  
Temperature Dependence ◽  
Temperature Effect ◽  
Isotope Effects ◽  
Benzyl Bromide ◽  
Kinetic Isotope Effects ◽  
Effect Of Temperature ◽  
Large Temperature ◽  
Bimolecular Reactions ◽  
Kinetic Isotope ◽  
Benzyl Halides

The temperature dependence of the 13C kinetic isotope of the α-carbon in benzyl bromide (1) and in 1-bromo-1-phenylethane (2) has been measured for reaction with alkoxide ion. For these bimolecular displacements, a relatively large temperature effect was found, comparable to that reported for other SN2 processes. A reexamination of the reaction of 2 with EtO− has shown an earlier value for k12/k13 to be in error.

scholarly journals Horseradish peroxidase. XXIX. Reactions in water and deuterium oxide: cyanide binding, compound I formation, and reactions of compounds I and II with ferrocyanide

1978 ◽  
Vol 56 (22) ◽  
pp. 2844-2852 ◽  
Author(s):  
H. Brian Dunford ◽  
W. Donald Hewson ◽  
Håkan Steiner
Keyword(s):  
Hydrogen Peroxide ◽  
Horseradish Peroxidase ◽  
Kinetic Isotope Effect ◽  
Deuterium Oxide ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Compound I ◽  
Kinetic Isotope ◽  
Cyanide Binding ◽  
Compound Ii

The kinetics of the reactions of hydrogen peroxide and cyanide with native horseradish peroxidase, as well as reactions of compounds I and II with ferrocyanide have been studied in ordinary water and in deuterium oxide at 25 °C and ionic strength 0.11 using a stopped-flow apparatus. Rate constants for all reactions were measured over a wide range of acidity in both solvents from which equilibrium and kinetic isotope effects were evaluated. Protonation of an ionizable group on the enzyme with a pKa value of 4.15 ± 0.05 in water inhibits the reactions with both hydrogen peroxide and cyanide. A significant kinetic isotope effect, kH/kD = 1.6 ± 0.1, was measured for compound I formation whereas no significant kinetic isotope effect was found for cyanide binding. On the basis of these findings, a partial mechanism for compound I formation is proposed in which the group of pKa 4.15 plays a crucial role. The pH dependencies of the ferrocyanide reaction in the pH interval 4.5–10.8 confirmed the role of an acid group with a pKa of 5.2 for compound I and for compound II a pKa of 8.6 and another with a value lower than that encompassed by the pH range of the study. Equilibrium isotope effects were found but no kinetic isotope effects for either the reaction of compound I or of compound II This suggests that there are no rate-limiting proton transfers in the reactions between ferrocyanide and compounds I and II of horseradish peroxidase. The only reducing substrates which exhibit positive kH/kD values possess a labile proton.

Model Calculations of Kinetic Isotope Effects in Nucleophilic Substitution Reactions

1974 ◽  
Vol 52 (6) ◽  
pp. 903-909 ◽  
Author(s):  
Jan Bron
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Benzyl Bromide ◽  
Kinetic Isotope Effects ◽  
Substitution Reactions ◽  
Model Calculations ◽  
Kinetic Isotope ◽  
Proposed Model ◽  
Standard Reaction ◽  
Deuterium Isotope Effects

The results of calculations indicate that a previously proposed model for the transition state in "borderline" substitution reactions can be generalized and, as a result, the observed differences in the carbon-13 and deuterium isotope effects of SN1, SN2, and "borderline" reactions rationalized. Although the conclusions may apply more generally, the standard reaction investigated is the solvolysis of benzyl bromide. The importance of resonance interaction with the phenyl ring, the significance of the product- or reactant-like character of the transition state, and the influence of the magnitude of force constants in determining isotope effects are examined. The temperature dependence of kinetic isotope effects in solvolysis is also investigated.

Secondary Kinetic Isotope Effects in Oxidative Addition of Benzyl Bromide to Dimethylplatinum(II) Complexes

2013 ◽  
Vol 32 (9) ◽  
pp. 2593-2598 ◽  
Author(s):  
Marzieh Dadkhah Aseman ◽  
Mehdi Rashidi ◽  
S. Masoud Nabavizadeh ◽  
Richard J. Puddephatt
Keyword(s):  
Isotope Effects ◽  
Oxidative Addition ◽  
Benzyl Bromide ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope

Theoretical Simulations of Heavy-Atom Kinetic Isotope Effects in Aliphatic Claisen Rearrangement

2020 ◽  
Vol 124 (51) ◽  
pp. 10678-10686
Author(s):  
Yuqing Xu ◽  
Kin-Yiu Wong ◽  
Meishan Wang ◽  
Desheng Liu ◽  
Wenkai Zhao ◽  
...  
Keyword(s):  
Claisen Rearrangement ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Theoretical Simulations
Sign in / Sign up

Export Citation Format

Share Document