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.

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. V. The Role of the Solvent in the Reaction Between Methyl Iodide and Pyridine

1972 ◽  
Vol 50 (7) ◽  
pp. 982-985 ◽  
Author(s):  
K. T. Leffek ◽  
A. F. Matheson
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
State Structure ◽  
Transition State Structure ◽  
Initial State ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects

Secondary kinetic deuterium isotope effects are presented for the reaction of methyl-d3 iodide and pyridine in four different solvents. Calculations on mass and moment of inertia change with deuteration in the initial state and an assumed tetrahedral transition state, together with internal rotational effects, are used to rationalize the inverse isotope effects. It is concluded from the variation of the isotopic rate ratio, that the transition state structure varies with solvent.

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.

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.

scholarly journals Secondary kinetic isotope effects in bimolecular nucleophilic substitutions. III. Deuterium effects in the Bunte salt reaction of methyl halides and sulfonates

1969 ◽  
Vol 47 (9) ◽  
pp. 1537-1541 ◽  
Author(s):  
G. E. Jackson ◽  
K. T. Leffek
Keyword(s):  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Conductivity Measurements ◽  
Nucleophilic Substitutions ◽  
Reaction Conditions ◽  
Methyl Halides ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
The Difference

Secondary kinetic deuterium isotope effects have been measured for the reaction between thiosulfate ion and methyl-d3 halides and sulfonates in 50% v/v ethanol–water. The results are used to extend the correlation of Seltzer of kH/kD with the difference between the polarizabilities of the attacking nucleophile and the leaving group.Dissociation constants for the [NaS2O3]− ion have been determined by conductivity measurements for the reaction conditions and used to calculate the concentration of free thiosulfate ions present in the reaction mixture. The activation parameters ΔH≠ and ΔS≠, based on second order rate constants calculated with respect to the concentration of thiosulfate ion, are reported.

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.

SOME DEUTERIUM KINETIC ISOTOPE EFFECTS: IV. β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ETHYL, ISOPROPYL, AND tert-BUTYL COMPOUNDS

1960 ◽  
Vol 38 (11) ◽  
pp. 2171-2177 ◽  
Author(s):  
K. T. Leffek ◽  
J. A. Llewellyn ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
Tert Butyl ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Intramolecular Forces

The secondary β-deuterium isotope effects have been measured in the water solvolytic reaction of alkyl halides and sulphonates for primary, secondary, and tertiary species. In every case the kinetic isotope effect was greater than unity (kH/kD > 1). This isotope effect may be associated with varying degrees of hyperconjugation or altered non-bonding intramolecular forces. The experiments make it difficult to decide which effect is most important.

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