DEUTERIUM KINETIC ISOTOPE EFFECTS: V TEMPERATURE DEPENDENCE OF β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ISOPROPYL COMPOUNDS

1961 ◽  
Vol 39 (10) ◽  
pp. 1989-1994 ◽  
Author(s):  
K. T. Leffek ◽  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Kinetic Isotope Effects ◽  
Methyl Groups ◽  
Deuterium Isotope Effect ◽  
Point Energy ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation

The secondary β-deuterium isotope effect (kH/kD) has been measured over a range of temperature for the water solvolysis reactions of isopropyl methanesulphonate, p-toluenesulphonate, and bromide. In these cases the isotope effect is due to a difference in entropies of activation of the isotopic analogues rather than a difference in the enthalpies of activation. It is suggested that the observed isotope effect is due to internal rotational effects of the methyl groups in the isopropyl radical, and the lack of an isotope effect on the enthalpy of activation is accounted for by a cancellation of an effect from this source and one from zero-point energy.

Unequal primary kinetic isotope effects in the base-catalysed H–D exchange of diastereotopic protons

1980 ◽  
Vol 58 (1) ◽  
pp. 72-78 ◽  
Author(s):  
Robert R. Fraser ◽  
Philippe J. Champagne
Keyword(s):  
Transition State ◽  
Exchange Reaction ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Deuterium Isotope Effect ◽  
Kinetic Isotope

Primary kinetic isotope effects have been measured for the base-catalyzed exchange reaction of 4′,1″-dimethyl-1,2,3,4-dibenzcyclohepta-1,3-diene-6-one, 1. It was found that the isotope effects kH/kT and kD/kT for the faster exchanging protons (13.6 and 3.8 respectively) are significantly larger than the corresponding values for the slower exchanging protons (4.6 and 1.6 respectively). These differences could result from truly unequal isotope effects due to transition state differences or intrusion of a second pathway for exchange of the less reactive proton in the dedeuteration reaction. The data appear to support the latter interpretation. The secondary deuterium isotope effect was found to be 1.18.

THE MECHANISM OF THE CARBONYL ELIMINATION REACTION OF BENZYL NITRATE KINETIC ISOTOPE EFFECTS AND DEUTERIUM EXCHANGE

1960 ◽  
Vol 38 (12) ◽  
pp. 2457-2466 ◽  
Author(s):  
Erwin Buncel ◽  
A. N. Bourns
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Kinetic Isotope Effects ◽  
Deuterium Exchange ◽  
Elimination Reaction ◽  
Deuterium Isotope Effect ◽  
Nitrite Ion ◽  
Kinetic Isotope ◽  
Reaction Constant

The carbonyl elimination reaction (ECO2) of benzyl nitrate has been investigated with the object of distinguishing between the concerted and carbanion mechanisms. A deuterium exchange experiment resulted in a very small amount of deuterium pickup. The nitrogen isotope effect, k14/k15, associated with formation of the nitrite ion was found to be 1.0196 ± 0.0007 at 30 °C. The two results taken together exclude the formation of a carbanion intermediate but are consistent with a concerted mechanism.Benzyl-α-d2 nitrate has been prepared and the rate of its carbonyl elimination reaction compared with that of the undeuterated compound. The deuterium isotope effect was 5.04 ± 0.25 at 60 °C. The significance of the magnitude of the nitrogen and deuterium isotope effects and of their interrelationship with the Hammett reaction constant rho is discussed in terms of the nature of the transition state and a comparison is made with other E2 elimination reactions.

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. IV. The Temperature Dependence of the Deuterium Effect for the Reaction of N,N-Dimethyl-d6-aniline and Methyl p-toluenesulfonate. Correlation of Isotope Effects on Activation Parameters

1971 ◽  
Vol 49 (3) ◽  
pp. 439-446 ◽  
Author(s):  
K. T. Leffek ◽  
A. F. Matheson
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Similar Correlation ◽  
Straight Lines

The temperature dependence of the isotope effect for the reaction of dimethylaniline and dimethyl-d6-aniline with methyl p-toluenesulfonate in nitrobenzene solvent has been measured, yielding the result, (ΔHD* − ΔHH*) = −134 ± 30 cal mole−1, (ΔSD* − ΔSH*) = −0.15 ± 0.09 cal mol–1 degree−1.This result has been compared with 15 other temperature dependence studies by plotting ΔΔH* per D atom vs. TΔΔS* per D atom. The points fall on two clearly separated straight lines. A similar correlation is found for a plot of ΔΔG* per D atom vs. ΔΔH* per D atom.The significance of the correlation is discussed and a possible rationalization, in terms of mechanism and particularly the role of the solvent is given.

Carbon-13 kinetic isotope effects. III. Temperature dependence of k12/k13 for 1-bromo-1-phenylethane alcoholysis

1968 ◽  
Vol 46 (8) ◽  
pp. 1435-1439 ◽  
Author(s):  
Jan Bron ◽  
J. B. Stothers
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope ◽  
Increasing Temperature

The temperature dependence of k12/k13 for methanolysis and ethanolysis at the α-carbon of 1-bromo-1-phenylethane has been determined over the ranges 25° and 45° respectively. It is found that the kinetic isotope effect increases with increasing temperature for these systems. This result offers support for earlier interpretations on the 13C fractionations measured previously and the data are considered in terms of the original Bigeleisen equation. The results indicate that primary kinetic 13C isotope effects may be useful for distinguishing between bimolecular and unimolecular substitution mechanisms.

Competitive photochlorination and kinetic isotope effects for hydrogen/deuterium abstraction from the methyl group in C2H6, C2D6, CH3CHCl2, CD3CHCl2, CH3CCl3, and CD3CCl3

1985 ◽  
Vol 63 (5) ◽  
pp. 1093-1099 ◽  
Author(s):  
E. Tschuikow-Roux ◽  
Jan Niedzielski ◽  
F. Faraji
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Arrhenius Law ◽  
Chloromethyl Group ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Hydrogen Deuterium

The abstraction of hydrogen and deuterium from ethane, 1,1-dichloroethane, 1,1,1-trichloroethane, and some of their deuterated analogs by photochemically generated ground state chlorine atoms has been investigated in the temperature range 7–95 °C using methane as competitor. Rate constants and their temperature coefficients are reported for the following reactions:[Formula: see text]An Arrhenius law temperature dependence was observed in all cases. Mixed primary and α-secondary kinetic isotope effects are k1/k2 = 2.79 ± 0.27, k4/k6 = 4.13 ± 0.32, k7/k8 = 1.46 ± 0.12 at 298 K and decrease to k1/k2 = 2.53 ± 0.22, k4/k6 = 4.06 ± 0.28, k7/k8 = 1.45 ± 0.09 at 370 K, showing a "normal" temperature dependence. The kinetic isotope effect for H/D abstraction from the methyl group decreases with increasing number of chlorine substituents in the adjacent chloromethyl group. The β-secondary isotope effect, k3/k5, is close to unity and shows a slight inverse temperature dependence.

Secondary Isotope Effects on the Ionization of 2-Nitropropane

1974 ◽  
Vol 52 (10) ◽  
pp. 1889-1896 ◽  
Author(s):  
A. J. Kresge ◽  
D. A. Drake ◽  
Y. Chiang
Keyword(s):  
Aqueous Solution ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Acid Dissociation ◽  
Methyl Groups ◽  
Anomalous Effect ◽  
Hydroxide Ion ◽  
Kinetic Isotope

The equilibrium isotope effect on the acid dissociation of 2-nitropropane in wholly aqueous solution at 25° was found to be KH/KD = 1.23 ± 0.03 for complete deuteration of both methyl groups; the kinetic isotope effect for reaction of the same substrate with hydroxide ion, kH/kD = 1.09 ± 0.01; and the kinetic isotope effect for reaction with tris-(hydroxymethyl)-methylamine, kH/kD = 1.10 ± 0.01; both of the latter also refer to wholly aqueous solution at 25° and are for complete deuteration of both methyl groups. It is shown that the equilibrium isotope effect is largely, and the kinetic isotope effects probably partly, hyper conjugative in origin, thus supporting a hyper conjugative explanation of the anomalous effect of methyl groups on nitroalkane ionization.

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