Vinyl Proton Abstraction during Metalation of α-Olefins

1963 ◽  
Vol 28 (5) ◽  
pp. 1174-1179 ◽  
Author(s):  
C. D. Broaddus ◽  
T. J. Logan ◽  
T. J. Flautt
Keyword(s):  
Vinyl Proton ◽  
Proton Abstraction

scholarly journals Kinetics and Mechanism of the Change of the 4-Nitrobenzylthio-System into 4,4′-Diformylazoxybenzene in Alkaline Dioxane-Water Media

1985 ◽  
Vol 40 (11) ◽  
pp. 1128-1132
Author(s):  
Y. Riad ◽  
Adel N. Asaad ◽  
G.-A. S. Gohar ◽  
A. A. Abdallah
Keyword(s):  
Acetic Acid ◽  
Sodium Hydroxide ◽  
Rate Constants ◽  
Main Product ◽  
Reaction Medium ◽  
Aqueous Dioxane ◽  
Proton Abstraction ◽  
First Order ◽  
Water Media ◽  
Different Temperatures

Sodium hydroxide reacts with α -(4-nitrobenzylthio)-acetic acid in aqueous-dioxane media to give 4,4'-diformylazoxybenzene as the main product besides 4,4'-dicarboxyazoxybenzene and a nitrone acid. This reaction was kinetically studied in presence of excess of alkali in different dioxane-water media at different temperatures. It started by a fast reversible a-proton abstraction step followed by two consecutive irreversible first-order steps forming two intermediates (α -hydroxy, 4-nitrosobenzylthio)-acetic acid and 4-nitrosobenzaldehyde. The latter underwent a Cannizzaro's reaction, the products of which changed in the reaction medium into 4,4'-diformylazoxybenzene and 4,4'-dicarboxyazoxybenzene. The rate constants and the thermodynamic parameters of the two consecutive steps were calculated and discussed. A mechanism was put forward for the formation of the nitrone acid.Other six 4-nitrobenzyl, aryl sulphides were qualitatively studied and they gave mainly 4,4'-diformylazoxybenzene beside 4,4'-dicarboxyazoxybenzene or its corresponding azo acid.

The Mechanism of Sugar C−H Bond Oxidation by a Flavoprotein Oxidase Occurs by a Hydride Transfer Before Proton Abstraction

2019 ◽  
Vol 25 (17) ◽  
pp. 4460-4471 ◽  
Author(s):  
Thanyaporn Wongnate ◽  
Panida Surawatanawong ◽  
Litavadee Chuaboon ◽  
Narin Lawan ◽  
Pimchai Chaiyen
Keyword(s):  
Hydride Transfer ◽  
Proton Abstraction

scholarly journals l-mandelate dehydrogenase from Rhodotorula graminis: comparisons with the l-lactate dehydrogenase (flavocytochrome b2) from Saccharomyces cerevisiae

1993 ◽  
Vol 290 (1) ◽  
pp. 103-107 ◽  
Author(s):  
O Smékal ◽  
M Yasin ◽  
C A Fewson ◽  
G A Reid ◽  
S K Chapman
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Lactate Dehydrogenase ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Dimensional Structure ◽  
Striking Difference ◽  
Kinetic Properties ◽  
Proton Abstraction ◽  
Rate Determining Step ◽  
Kinetic Isotope

L-Lactate dehydrogenase (L-LDH) from Saccharomyces cerevisiae and L-mandelate dehydrogenase (L-MDH) from Rhodotorula graminis are both flavocytochromes b2. The kinetic properties of these enzymes have been compared using steady-state kinetic methods. The most striking difference between the two enzymes is found by comparing their substrate specificities. L-LDH and L-MDH have mutually exclusive primary substrates, i.e. the substrate for one enzyme is a potent competitive inhibitor for the other. Molecular-modelling studies on the known three-dimensional structure of S. cerevisiae L-LDH suggest that this enzyme is unable to catalyse the oxidation of L-mandelate because productive binding is impeded by steric interference, particularly between the side chain of Leu-230 and the phenyl ring of mandelate. Another major difference between L-LDH and L-MDH lies in the rate-determining step. For S. cerevisiae L-LDH, the major rate-determining step is proton abstraction at C-2 of lactate, as previously shown by the 2H kinetic-isotope effect. However, in R. graminis L-MDH the kinetic-isotope effect seen with DL-[2-2H]mandelate is only 1.1 +/- 0.1, clearly showing that proton abstraction at C-2 of mandelate is not rate-limiting. The fact that the rate-determining step is different indicates that the transition states in each of these enzymes must also be different.

Kinetic and Equilibrium Studies of the Reactions of 2,4,6-Trinitrotoluene and 2,4,6-Trinitrotoluene-d3 with Sodium and Potassium t-Butoxide in t-Butanol

1974 ◽  
Vol 52 (12) ◽  
pp. 2306-2315 ◽  
Author(s):  
Erwin Buncel ◽  
Albert Richard Norris ◽  
Kenneth Edwin Russell ◽  
Harold Wilson
Keyword(s):  
Initial Rate ◽  
Forward Rate ◽  
Specific Rate ◽  
Equilibrium Studies ◽  
Proton Abstraction ◽  
Kinetic Isotope ◽  
Forward Rate Constant ◽  
Hydrogen Deuterium ◽  
Reaction In Solution ◽  
Sodium And Potassium

The reactions of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrotoluene fully deuterated at the methyl position (TNT-d3) with sodium and potassium t-butoxide in t-butanol have been studied. With TNT as the substrate, proton abstraction by ion-paired sodium or potassium t-butoxide appears to be the predominant reaction in solution. With sodium t-butoxide as base, the forward rate constant for proton abstraction at 30.0 °C (Kf,ip) is 6000 ± 400 M−1 s−1 while ΔH≠ and ΔS≠ for the reaction are 4.2 ± 0.3 kcal mol−1 and −27 ± 2 cal deg−1 mol−1, respectively. With TNT-d3 as the substrate, formation of a TNT-d3-t-butoxide ion σ-complex occurs simultaneously with deuteron abstraction. Specific rate constants for the two processes have been determined at 30.0 °C. Initial rate studies establish a hydrogen-deuterium kinetic isotope effect of 8 ± 1 for the formation of the anion in t-butanol.

Fragmentation of alkoxide ions following collisional activation. An energy-resolved study

1988 ◽  
Vol 66 (11) ◽  
pp. 2947-2953 ◽  
Author(s):  
Roger S. Mercer ◽  
Alex G. Harrison
Keyword(s):  
Kinetic Energy ◽  
Collisional Activation ◽  
Collision Energy ◽  
Relative Importance ◽  
Elimination Reaction ◽  
Proton Abstraction ◽  
Relative Stabilities ◽  
Collisionally Activated Dissociation ◽  
Reaction Channels ◽  
Alkane Elimination

The collisionally activated dissociation reactions of the C2 to C5 alkoxide ions have been studied for collisons occurring at 8 keV kinetic energy and also over the range 5 to 100 eV kinetic energy. The alkoxide ions fragment by 1,2-elimination of H2 and/or an alkane. Thus, primary alkoxide ions fragment by elimination of H2 only, secondary alkoxide ions show elimination of H2 and alkane molecules, while tertiary alkoxide ions show elimination of alkanes only. In alkane elimination, loss of CH4 is much more facilie than loss of larger alkanes. For secondary alkoxide ions, where more than one elimination reaction occurs, the energy dependence of fragmentation has been explored over the collision energy range 5 to 100 eV. The results are interpreted in terms of a step-wise mechanism involving formation of an anion-carbonyl compound ion-dipole complex, followed by proton abstraction by the H− or alkyl anion leading to the final products. The relative importance of the reaction channels is determined by the relative stabilities of these ion-dipole complexes.

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