A Primary Hydrogen-Deuterium Isotope Effect Study on the Carbonyl Elimination Reaction of 9-Fluorenyl Nitrate with Various Bases

1975 ◽  
Vol 53 (2) ◽  
pp. 263-268 ◽  
Author(s):  
Peter James Smith ◽  
Lorraine Marion Noble
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Effect Study ◽  
Elimination Reaction ◽  
Deuterium Isotope Effect ◽  
Nitrogen Bases ◽  
Transition State Geometry ◽  
Hydrogen Deuterium ◽  
Deuterium Isotope Effects

The carbonyl elimination reaction of 9-fluorenyl nitrate with various nitrogen bases in anhydrous ethanol at 0 °C was examined. In all cases fluorenone was formed in 100% yield indicating that there was not any substitution. A reasonable Brønsted plot was obtained for reaction promoted by structurally similar bases with β = 0.84 which suggests a product-like transition state. As well, deviations from the Brønsted plot are discussed. Primary hydrogen-deuterium isotope effects were measured for reaction promoted by 11 different amine bases. A reasonable correlation was obtained for structurally similar bases when a plot of kH/kDvs. pKa was made. The conclusion is reached that when kH/kD reaches a maximum, ∼9.2 at 0 °C, it remains unchanged and hence is a poor measure of transition state geometry. As well, very poor correlations are found when the abstracting base is tertiary which leads to the conclusion that a comparison of kH/kD values is not warranted for structurally different bases.

The Preparation and Acetolyses of 5-Deuteriated exo-2-Norbornyl-p-bromobenzenesulfonates

1972 ◽  
Vol 50 (5) ◽  
pp. 618-626 ◽  
Author(s):  
N. H. Werstiuk ◽  
R. R. MacDonald ◽  
R. W. Ouwehand ◽  
W. L. Chan ◽  
F. P. Cappelli ◽  
...  
Keyword(s):  
Experimental Evidence ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Deuterium Isotope Effect ◽  
Hydrogen Deuterium ◽  
Deuterium Isotope Effects

The deuterionorborneols 2a, b, c, and e have been prepared and converted to the brosylates 1a, b, c, and e. The deuterium isotope effects determined spectrophotometrically for solvolysis in HOAc–KOAc are 1.00 ± 0.01, 1.01 ± 0.01, 0.99 ± 0.01, and 1.11 ± 0.01, respectively. These data establish that: (a) a steric deuterium isotope effect does not operate at C-5 and therefore probably not at C-6; (b) hyperconjugative stabilization of the norbornonium ion to the C-5 hydrogens is confirmed to be not important, and (c) provides the first experimental evidence that the hydrogen (deuterium) shift – internal return pathway contribution to the γ-deuterium isotope effects observed for 1d and e is minor.

Isotope Effect Studies on Elimination Reactions. X. The Nature of The Transition State for the ECO2 Reaction of Para- substituted Benzyl Nitrates with Base in 90% by Volume Ethanol–Water

1975 ◽  
Vol 53 (9) ◽  
pp. 1319-1326 ◽  
Author(s):  
Peter James Smith ◽  
Carol Audrey Pollock ◽  
Arthur Newcombe Bourns
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Kinetic Isotope Effects ◽  
The Other ◽  
Theoretical Treatment ◽  
Kinetic Isotope ◽  
Hydrogen Deuterium ◽  
Deuterium Isotope Effects

Kinetic isotope effects have been determined for the Eco2 reaction of para-substituted benzyl nitrates with ethoxide in 90 vol.% ethanol–water at 20°. The nitrogen isotope effect, (k14/k15−1)100 decreased with increasing electron-withdrawing ability of the para-substituent; i.e. 2.26, 1.95, 1.60, and 0.84 for p-CH3, p-H, p-CF3, and p-NO2, respectively. Furthermore, the primary hydrogen–deuterium isotope effects increased also for electron-withdrawing substituents; i.e. kH/kD = 5.78, 6.06, 6.40, 6.67, and 7.05 for p-CH3, p-H, p-Br, p-CF3, and p-NO2, respectively. The results are discussed in terms of a recent theoretical treatment dealing with the effect of substituents on the nature of the transition state for a concerted E2 process. The conclusion is reached that any structural change which causes one bond (carbon–hydrogen) to be weakened more at the transition state will have a corresponding effect on the other bond (oxygen–nitrogen).

2,4-Diazapentadienes. II. A Carbanion Cyclization

1972 ◽  
Vol 50 (5) ◽  
pp. 678-689 ◽  
Author(s):  
D. H. Hunter ◽  
S. K. Sim
Keyword(s):  
Isotope Effect ◽  
Solvent Effects ◽  
Isotope Effects ◽  
Substituent Effects ◽  
Deuterium Exchange ◽  
Hydrogen Deuterium Exchange ◽  
Deuterium Isotope Effect ◽  
Potassium Methoxide ◽  
Proton Shift ◽  
Hydrogen Deuterium

The mechanism of the cyclization and 1,3-proton shift of 1,3,5-triaryl-2,4-diaza-1,3-pentadienes (1) catalyzed by phenyllithium and by potassium methoxide–methanol has been studied. On the basis of substituent effects, hydrogen–deuterium exchange, isotope effects, and solvent effects, it was deduced that both the cyclization and prototropy involve a common W-shaped carbanion which rapidly cyclizes. A kinetic deuterium isotope effect of 2 was calculated for protonation of this intermediate carbanion in methanol.

Isotope Effect Studies on Elimination Reactions. XI. The Nature of the Transition State for the E2 Reaction of 2-Phenylethyldimethylanilinium Salts Containing Substituents in the Aniline Ring with Sodium Ethoxide in Ethanol

1975 ◽  
Vol 53 (23) ◽  
pp. 3513-3525 ◽  
Author(s):  
Peter Schmid ◽  
Arthur Newcombe Bourns
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Structural Changes ◽  
Isotope Effects ◽  
Sodium Ethoxide ◽  
Nitrogen Isotope ◽  
Structural Variations ◽  
Hydrogen Deuterium ◽  
Elimination Reactions ◽  
Pass Through

Kinetic isotope effects have been determined for the E2 reactions of a series of 2-phenylethyldimethylanilinium salts containing substituents in the aniline ring with sodium ethoxide in ethanol at 40 °C. The nitrogen isotope effect, (k14/k15−1)100, is not very sensitive to substituent changes but appears to increase slightly with increasing electron-withdrawing ability of the substituents, i.e., 1.19 ± 0.07, 1.13 ± 0.06, 1.12 ± 0.08, 1.30 ± 0.07, and 1.32 ± 0.06 for p-OCH3, p-CH3, p-H, p-Cl, and, m-CF3, respectively. The hydrogen–deuterium isotope effects pass through a minimum in the region of the unsubstituted compound and increase both with increasing electron-donating as well as with electron-withdrawing power of the substituents, i.e. kH/kD = 4.70 ± 0.06, 4.61 ± 0.04, 4.51 ± 0.04, 4.53 ± 0.09, 5.00 ± 0.07, and 5.39 ± 0.07 for p-OCH3, p-CH3, p-H, p-Cl, m-CF3, and p-CF3, respectively. The results are discussed in terms of recent theoretical treatments of the effect of structural variations in the reactants on the nature of the transition state of E2 elimination reactions. The conclusion is reached that the transition states in the present reaction series can be characterized as 'central with slight carbanion character' and that the effect of a change in the ability of the leaving group on the structure of the transition state manifests itself mainly in the direction perpendicular to the reaction coordinate. A simple novel hypothesis is formulated which emphasizes the importance of the location of the transition state in a More O'Ferrall-type potential energy diagram in determining its sensitivity to structural changes in the reactants.

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.

scholarly journals Deuterium Isotope Effects in the Oxidation of 2,3-Dimethyl-2-butene via the Bromohydroperoxide, by Singlet Oxygen and by Triphenyl Phosphite Ozonide

1972 ◽  
Vol 50 (24) ◽  
pp. 4034-4049 ◽  
Author(s):  
Karl R. Kopecky ◽  
Johan H. van de Sande
Keyword(s):  
Singlet Oxygen ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Bond Breaking ◽  
Triphenyl Phosphite ◽  
Deuterium Isotope Effect ◽  
Major Isomer ◽  
Deuterium Isotope Effects ◽  
Oxygen Oxidation ◽  
Cis And Trans

The partially deuterated alkenes (CH3)2C = C(CD3)2 (1b) and CH3CD3C = CCH3CD3 (1c) were prepared and converted to the corresponding allylic hydroperoxides by the routes shown in the title. Two bromohydroperoxides were formed from 1b in a 1.6:1 ratio with the major isomer having the OOH group on the carbon bearing the CH3's. On treatment with base at 0° this mixture formed two allylic hydroperoxides in a 2.2:1 ratio with the major isomer having the OOH group on the carbon bearing the CD3's, showing migration of the OOH group. This isomer predominated in a 1.4:1 ratio when 1b was oxidized with singlet oxygen at 15 or −52° and in a 1.6:1 ratio when 1b was oxidized with triphenyl phosphite ozonide at −70°. Under the same conditions C—H bond breaking also predominated in the oxidation of 1c, by 2.1:1 via the bromohydroperoxide, by 1.4:1 with singlet oxygen, and by 1.3:1 with triphenyl phosphite ozonide. Migration of the OOH group in the reaction of the bromohydroperoxide of 1b does not occur by way of a 1,2-dioxetane. A perepoxide may be the intermediate. Neither perepoxides nor 1,2-dioxetanes are involved in the singlet oxygen oxidation of 1b and c. At −70° the triphenyl phosphite ozonide oxidations do not proceed by way of these intermediates, either, or by way of singlet oxygen. The intermolecular deuterium isotope effect in the singlet oxygen oxidation of both cis- and trans-2,3-diphenyl-2-butene was found to be 1.1.

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

1972 ◽  
Vol 50 (3) ◽  
pp. 388-394 ◽  
Author(s):  
Donald C. Wigfield ◽  
David J. Phelps
Keyword(s):  
Product Development ◽  
Transition State ◽  
Isotope Effect ◽  
Steric Hindrance ◽  
Isotope Effects ◽  
Development Control ◽  
Control Product ◽  
Deuterium Isotope Effects ◽  
Early Transition

Definitions for the terms stericapproachcontrol and productdevelopmentcontrol in relation to the degree of bonding in the transition state are put forward. Kinetic deuterium isotope effects in the reduction of a graded series of ketones by NaBH4 and NaBD4 have been measured. These effects are inverse, and show no systematic dependence on the degree of steric hindrance of the ketone. This evidence appears to invalidate the steric approach control – product development control explanation of the axial to equatorial product ratios (1). The primary isotope effect is very small, which is consistent with an early transition state in these reductions, as demanded by other explanations of product ratios, but since several other factors causing small isotope effects may be applicable, the evidence does not constitute proof of an early transition state.The main conclusions of this work have already been published in preliminary form (2).

Isotope Effect Studies on Elimination Reactions. IX. The Nature of the Transition State for the E2 Reaction of 2-Arylethylammonium Ions with Ethoxide in Ethanol

1974 ◽  
Vol 52 (5) ◽  
pp. 749-760 ◽  
Author(s):  
P. J. Smith ◽  
A. N. Bourns
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Kinetic Isotope Effects ◽  
Ammonium Ions ◽  
Nitrogen Effect ◽  
Kinetic Isotope ◽  
Leaving Group ◽  
Hydrogen Deuterium

Kinetic isotope effects have been determined for the E2 reaction of some 2-arylethyltrimethyl-ammonium ions with ethoxide in ethanol at 40°. The nitrogen effect, (k14/k15 − 1)100, decreased with increasing electron-withdrawing ability of the para substituent; i.e. 1.37, 1.33, 1.14, and 0.88 for p-OCH3, p-H, p-Cl, and p-CF3, respectively. Furthermore, the primary hydrogen–deuterium isotope effects increased for the same substituents, respectively; i.e. kH/kD = 2.64, 3.23, 3.48, and 4.16. A large positive ρ value of 3.66 was found as well as a small secondary α-deuterium effect of 1.02 for p-H. In addition, the nitrogen isotope effect decreased with increasing strength of the abstracting base for the reaction of ethyltrimethylammonium ion; i.e. 1.86 and 1.41 at 60° for reaction with EtO−–EtOH and t-BuO−–t-BuOH, respectively. The results are discussed in terms of recent theoretical treatments of the effect of base, substituents, and nature of the leaving group on the nature of the transition state for an E2 process. The conclusion is reached that any structural change which causes one bond (C—H) to be weakened more at the transition state will have a corresponding effect on the other bond [Formula: see text]

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