SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: II. α-DEUTERIUM EFFECTS IN MENSCHUTKIN REACTIONS OF METHYL IODIDE

1965 ◽  
Vol 43 (1) ◽  
pp. 40-46 ◽  
Author(s):  
K. T. Leffek ◽  
J. W. MacLean
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Systematic Change ◽  
Tertiary Amines ◽  
Nucleophilic Substitutions ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Deuterium Substitution ◽  
Different Temperatures ◽  
Rate Ratios

Secondary deuterium isotope effects have been measured for the reactions between methyl and methyl-d3 iodides and a series of tertiary amines in benzene solvent. Deuterium substitution increased the rate of each reaction but the rate ratios (kH/kD) show no systematic change with variation in the structure of the amine. The isotope effect for the reaction with 2-picoline was measured at different temperatures over a range of 40 deg and shows no change. These isotope effects may be rationalized as internal rotational effects of the methyl group or as solvation effects.

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. VI. Effect of α and β Deuteration of Alkyl Halides in their Menschutkin Reactions with Pyridine in Nitrobenzene

1972 ◽  
Vol 50 (7) ◽  
pp. 986-991 ◽  
Author(s):  
K. T. Leffek ◽  
A. F. Matheson
Keyword(s):  
Isotope Effects ◽  
Side Reaction ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
State Structure ◽  
Transition State Structure ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Rate Ratios

A survey of kinetic, secondary deuterium isotope effects, for α, β, and γ deuterated alkyl halides reacting with pyridine in nitrobenzene solvent has been made. α-Deuterium effects have been measured for eight compounds, β-deuterium effects for four compounds, and one rate ratio for γ-deuteration is reported. The possible errors in the rate ratios for β-deuterated compounds, resulting from the elimination side reaction have been determined. The results are discussed in terms of transition state structure.

SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: I. DEUTERIUM EFFECTS IN THE BUNTE SALT REACTION

1964 ◽  
Vol 42 (4) ◽  
pp. 851-855 ◽  
Author(s):  
K. T. Leffek
Keyword(s):  
Aqueous Ethanol ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Sodium Thiosulphate ◽  
Deuterium Isotope Effect ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Rate Ratios ◽  
Aqueous Ethanol Solvent

The secondary deuterium isotope effects have been measured for the reaction between sodium thiosulphate and α-deuterated methyl, ethyl, and n-propyl bromide, and also for β- and γ-deuterated n-propyl bromide, in aqueous ethanol solvent. The α-deuterium isotopic rate ratios (kH/kD) are all greater than unity. These unexpected results are discussed with respect to the suggested use of the α-deuterium isotope effect as a test of mechanism in nucleophilic substitutions.

α-DEUTERIUM KINETIC ISOTOPE EFFECTS IN SOLVOLYSES OF endo-NORBORNYL p-BROMOBENZENESULFONATE

1965 ◽  
Vol 43 (8) ◽  
pp. 2254-2258 ◽  
Author(s):  
C. C. Lee ◽  
Edward W. C. Wong
Keyword(s):  
Acetic Acid ◽  
Formic Acid ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Aqueous Dioxane ◽  
Kinetic Isotope ◽  
Different Temperatures

endo-Norbornyl-2-d p-bromobenzenesulfonate was synthesized and the isotope effects, as measured by kH/kD, were determined over a range of temperatures for solvolyses in 30% water – 70% dioxane, acetic acid, and formic acid. Values of kH/kD are of the order of 1.20. The data appear to indicate slightly higher isotope effects as the solvents are changed from aqueous dioxane to acetic acid to formic acid, as well as somewhat higher isotope effects at lower temperatures. Possible mechanistic implications of these results are presented. Relative titrimetric acetolysis rates, kexo/kendo, at different temperatures, and enthalpies and entropies of activation for these acetolyses are evaluated and discussed.

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.

AROMATIC SUBSTITUTION: PART VIII. SOME ASPECTS OF THE MECHANISM OF THE TSCHITSCHIBABIN REACTION

1965 ◽  
Vol 43 (4) ◽  
pp. 725-731 ◽  
Author(s):  
R. A. Abramovitch ◽  
F. Helmer ◽  
J. G. Saha
Keyword(s):  
Molecular Orbital ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Aromatic Substitution ◽  
Direct Amination ◽  
Detailed Mechanism ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Rule Out

The mechanism of the direct amination of pyridines is discussed in terms of both addition–elimination and elimination–addition pathways. The absence of deuterium kinetic isotope effects as well as the orientations observed in such reactions rule out the intervention of 2,3- or 2,6-dehydropyridines. The effect of a 3-methyl group upon the reactivities towards the amide ion of the various nuclear positions in pyridine has been determined. Predictions based on molecular orbital (m.o.) calculations are discussed in terms of the detailed mechanism of this reaction and of the orientations observed.

scholarly journals Formation of Enamines via Catalytic Dehydrogenation by Pincer-Iridium Complexes

2019 ◽  
Author(s):  
Xiawei Zhang ◽  
Santanu Malakar ◽  
Karsten Krogh-Jespersen ◽  
Faraj Hasanayn ◽  
Alan Goldman
Keyword(s):  
Isotope Effects ◽  
Oxidative Addition ◽  
Kinetic Isotope Effects ◽  
Catalytic Dehydrogenation ◽  
Iridium Complexes ◽  
Tertiary Amines ◽  
Iridium Catalysts ◽  
Kinetic Isotope ◽  
Dehydrogenation Mechanism

Efficient pincer-ligated iridium catalysts are reported for the dehydrogenation of simple tertiary amines to give enamines, and for the dehydrogenation of β-functionalized amines to give the corresponding 1,2-difunctionalized olefins. Experimentally determined kinetic isotope effects in conjunction with DFT-based analysis support a dehydrogenation mechanism involving initial pre-equilibrium oxidative addition of the amine α C-H bond followed by rate-determining elimination of the β-C-H bond.<br>

scholarly journals Formation of Enamines via Catalytic Dehydrogenation by Pincer-Iridium Complexes

2019 ◽  
Author(s):  
Xiawei Zhang ◽  
Santanu Malakar ◽  
Karsten Krogh-Jespersen ◽  
Faraj Hasanayn ◽  
Alan Goldman
Keyword(s):  
Isotope Effects ◽  
Oxidative Addition ◽  
Kinetic Isotope Effects ◽  
Catalytic Dehydrogenation ◽  
Iridium Complexes ◽  
Tertiary Amines ◽  
Iridium Catalysts ◽  
Kinetic Isotope ◽  
Dehydrogenation Mechanism

Efficient pincer-ligated iridium catalysts are reported for the dehydrogenation of simple tertiary amines to give enamines, and for the dehydrogenation of β-functionalized amines to give the corresponding 1,2-difunctionalized olefins. Experimentally determined kinetic isotope effects in conjunction with DFT-based analysis support a dehydrogenation mechanism involving initial pre-equilibrium oxidative addition of the amine α C-H bond followed by rate-determining elimination of the β-C-H bond.<br>

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.

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