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.

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]

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).

The effect of the nature of the amine leaving group on the nature of the E2 transition state for the reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol

1989 ◽  
Vol 67 (9) ◽  
pp. 1457-1467 ◽  
Author(s):  
Peter James Smith ◽  
Md. Amin
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Sodium Ethoxide ◽  
Elimination Process ◽  
Leaving Group ◽  
Hydrogen Deuterium ◽  
Mechanism Transition ◽  
Leaving Groups ◽  
Leaving Group Ability

To investigate the effect of the leaving group on the elimination reaction of 1-phenylethylammonium ions with sodium ethoxide in ethanol at 60 °C, the reaction of seven different quaternary ammonium salts and their β-deuterated analogues with trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, N,N-dimethylbenzylamine, tripropylamine, and N,N-diethylbenzylamine as leaving groups has been studied. In all cases the elimination, which was shown to proceed via the concerted E2 process, was accompanied by competing substitution reactions. Although a significant dependence of the rate of the elimination process on the nature of the leaving group was noted, there was not any linear correlation with the basicity of the amine leaving group. The primary hydrogen–deuterium kinetic isotope effect for the elimination process, (kH/kD)E, was found to increase initially with an increase of reaction rate, [Formula: see text] for substrates containing the leaving groups trimethylamine, N-methylpiperidine, N-methyldiethylamine, triethylamine, and N,N-dimethylbenzylamine; i.e., (kH/kD)E = 5.03, 5.26, 5.40, 5.83, and 5.85, respectively. A further increase in rate, using substrates with tripropylamine and N,N-diethylbenzylamine as leaving groups resulted in a decrease of the magnitude of the hydrogen–deuterium isotope effect; i. e., (kH/kD)E = 5.42 and 4.67, respectively. It is concluded that steric effects mainly determine leaving group ability. As well, it is concluded that the leaving group ability of the amine determines the structure of the E2 transition state. For the reaction of the poorer leaving groups, trimethylamine, N-methylpiperidine, and N-methyldiethylamine, the proton is morethan one-half transferred at the transition state while for reaction involving the two best leaving groups, tripropylamine and N,N-diethylbenzylamine, the Cβ—H bond is lessthan one-half broken at the transition state. The conclusions are considered in the light of the More O'Ferrall – Jencks potential energy surface diagram. Keywords: elimination mechanism, transition state, isotope effects, leaving group, quaternary salts.

The effect of steric crowding on an E2 transition state

1976 ◽  
Vol 54 (14) ◽  
pp. 2339-2341 ◽  
Author(s):  
George Stanley Dyson ◽  
Peter James Smith
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Nitrogen Isotope ◽  
Bond Rupture ◽  
Deuterium Isotope Effect ◽  
Steric Crowding ◽  
Reaction Proceeds ◽  
Hydrogen Deuterium ◽  
Nitrogen Bond ◽  
Mechanism Of The Reaction

The mechanism of the reaction of 9-(4-substituted benzyl)fluorene-9-trimethylammonium ions with ethoxide is a normal E2 process. The magnitude of the primary hydrogen–deuterium isotope effect at 60 °C increased with increasing electron-donating ability of the 4-substituent, i.e., 4.15, 5.10, 5.34, 5.65, 5.75, and 5.91 for the 4-CF3, 4-Br, 4-Cl, 4-H, 4-CH3, and 4-OCH3 substituents, respectively. The magnitude of the nitrogen isotope effect at 70 °C decreased with increased electron-donating power of the 4-substituent, i.e., [(k14/k15)–1]100 = 1.24, 0.95, 0.92, 0.91, and 0.80 for the 4-CF3, 4-F, 4-H, 4-CH3, and 4-OCH3 substituents, respectively. A small Hammett ρ value of +1.33 was observed for the reaction. It is concluded that the reaction proceeds via a transition state where the proton is more than one-half transferred to base. It is further concluded that for a reaction in which the 4-substituents decrease the rate, both carbon–hydrogen and carbon–nitrogen bond rupture is more advanced in the transition state. This variance with Hammond's postulate is discussed in the light of steric crowding at the transition state.

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.

Solvent effects on nucleophilic substitution reactions. III. The effect of adding an inert salt on the structure of the SN2 transition state

1996 ◽  
Vol 74 (12) ◽  
pp. 2528-2530 ◽  
Author(s):  
T.V. Pham ◽  
K.C. Westaway
Keyword(s):  
Ionic Strength ◽  
Transition State ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Kinetic Isotope Effects ◽  
Substitution Reactions ◽  
Kinetic Isotope ◽  
Ionic Transition ◽  
Hydrogen Deuterium ◽  
Inert Salt

The nitrogen and secondary α-hydrogen–deuterium kinetic isotope effects found for the SN2 reaction between thiophenoxide ion and benzyldimethylphenylammonium ion at different ionic strengths in DMF at 0 °C indicate that the structure of the transition state changes markedly with the ionic strength of the reaction mixture. In fact, a more reactant-like, more ionic, transition state is found at the higher ionic strength. This presumably occurs because a more ionic transition state is more stable in the more ionic solvent. Key words: transition state, ionic strength, secondary α deuterium kinetic isotope effects, nitrogen isotope effects, SN2.

ISOTOPE EFFECT STUDIES ON ELIMINATION REACTIONS: III. NITROGEN ISOTOPE EFFECTS IN THE E2 REACTION OF ETHYLTRIMETHYL-AMMONIUM AND 2-PHENYLETHYLTRIMETHYLAMMONIUM IONS

1963 ◽  
Vol 41 (7) ◽  
pp. 1759-1767 ◽  
Author(s):  
G. Ayrey ◽  
A. N. Bourns ◽  
V. A. Vyas
Keyword(s):  
Isotope Effect ◽  
Quaternary Ammonium ◽  
Isotope Effects ◽  
Transition States ◽  
Nitrogen Isotope ◽  
Quaternary Ammonium Salts ◽  
Ammonium Salts ◽  
Relative Extent ◽  
Deuterium Isotope Effects ◽  
Elimination Reactions

Nitrogen isotope effects have been determined for the E2 reaction of two quaternary ammonium salts with ethoxide ion in ethanol. Ethyltrimethylammonium iodide gave k14/k15 values of 1.017 at 60° and 1.015 at 95°, while 2-phenylethyltrimethylammonium bromide gave 1.012 at 40° and 1.009 at 60°. These results and the β-deuterium isotope effects reported by others have been interpreted in terms of the relative extent of Cα—N+ and Cβ—H bond weakening in the transition states of the two reactions.

Secondary α hydrogen–deuterium kinetic isotope effects in the syn-elimination reaction of 2-phenylethyldimethylamine oxide

1987 ◽  
Vol 65 (9) ◽  
pp. 2149-2153 ◽  
Author(s):  
Peter James Smith ◽  
Kenneth Charles Westaway
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Thermal Reaction ◽  
Bond Rupture ◽  
Elimination Process ◽  
Kinetic Isotope ◽  
Hydrogen Deuterium ◽  
Relative Transition

The secondary α-deuterium kinetic isotope effect has been measured for the thermal reaction of 2-phenylethyldimethylamine oxide in 90 mol% DMSO–H2O at 60.0 °C. A large secondary α-deuterium isotope effect of 1.158 per α-D was found, which indicates significant [Formula: see text] bond rupture and very little double bond formation at the transition state for this concerted syn-elimination process. The observed large normal value for (kH/kD)α is discussed in terms of the use of secondary α-D isotope effects for the determination of stereochemistry for a concerted elimination process. Various isotope effects found for the syn elimination of the above amine oxide and those for the anti elimination of 2-arylethyltrimethylammonium salts with ethoxide are considered with respect to the relative transition state structures for syn- and anti-elimination reactions.

scholarly journals Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Paul M. Magyar ◽  
Damian Hausherr ◽  
Robert Niederdorfer ◽  
Nicolas Stöcklin ◽  
Jing Wei ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Nitrogen Isotope ◽  
Anammox Bacteria ◽  
Ammonium Oxidation ◽  
Experimental Conditions ◽  
N Transformations ◽  
Natural Systems ◽  
Inverse Isotope Effect

AbstractAnaerobic ammonium oxidation (anammox) plays an important role in aquatic systems as a sink of bioavailable nitrogen (N), and in engineered processes by removing ammonium from wastewater. The isotope effects anammox imparts in the N isotope signatures (15N/14N) of ammonium, nitrite, and nitrate can be used to estimate its role in environmental settings, to describe physiological and ecological variations in the anammox process, and possibly to optimize anammox-based wastewater treatment. We measured the stable N-isotope composition of ammonium, nitrite, and nitrate in wastewater cultivations of anammox bacteria. We find that the N isotope enrichment factor 15ε for the reduction of nitrite to N2 is consistent across all experimental conditions (13.5‰ ± 3.7‰), suggesting it reflects the composition of the anammox bacteria community. Values of 15ε for the oxidation of nitrite to nitrate (inverse isotope effect, − 16 to − 43‰) and for the reduction of ammonium to N2 (normal isotope effect, 19–32‰) are more variable, and likely controlled by experimental conditions. We argue that the variations in the isotope effects can be tied to the metabolism and physiology of anammox bacteria, and that the broad range of isotope effects observed for anammox introduces complications for analyzing N-isotope mass balances in natural systems.

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