Fluorination observed Tc increase of 110 K is challenging the hydrogen–deuterium isotope effect

2019 ◽  
Vol 55 (67) ◽  
pp. 10007-10010 ◽  
Author(s):  
Yu-Ling Liu ◽  
Si-Qi Lu ◽  
Yuan-Yuan Tang ◽  
Xiao-Gang Chen ◽  
Ji-Xing Gao ◽  
...  
Keyword(s):  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Hydrogen Deuterium

The unprecedented Tc enhancement of 110 K observed with H/F substitution of [N-methyldabconium] triiodide lead is challenging the hydrogen–deuterium isotope effect.

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.

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.

Hydrogen‐deuterium isotope effect in the decay of radical pairs in x‐ray irradiated hydroxyurea

1974 ◽  
Vol 60 (1) ◽  
pp. 127-132 ◽  
Author(s):  
Ysbrand Haven ◽  
Rodney C. Williams ◽  
Phillip J. Hamrick ◽  
Howard Shields
Keyword(s):  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Radical Pairs ◽  
X Ray ◽  
Hydrogen Deuterium

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.

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