ISOTOPE EFFECTS IN NEUTRAL H2O–D2O IRRADIATED SOLUTIONS AND THE NATURE OF THE REDUCING RADICAL

1962 ◽  
Vol 40 (10) ◽  
pp. 1903-1908 ◽  
Author(s):  
Chava Lifshitz
Keyword(s):  
Hydrogen Atom ◽  
Water Molecule ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Sodium Formate ◽  
Alternative Possibilities ◽  
X Rays ◽  
Deuterium Isotope Effect ◽  
Deuterium Concentration ◽  
Single Water Molecule

Neutral solutions of sodium formate in H2O–D2O mixtures were irradiated by 200-kv X rays. The atomic deuterium isotope effect (αA) and its dependence on deuterium concentration were determined. In a 1 × 10−1 M HCOONa, 96% D2O solution, G(hydrogen) = 1.14 and αA = 4.3. It is concluded that the hydrogen atom cannot be formed from a single water molecule. Possible mechanisms of hydrogen atom formation are discussed. The alternative possibilities for the atoms to react as H or H2O− are viewed in the light of the proposed mechanisms.

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.

Stereochemistry of Dehydrogenation by D-Galactose Oxidase

1971 ◽  
Vol 49 (21) ◽  
pp. 3429-3437 ◽  
Author(s):  
A. Maradufu ◽  
G. M. Cree ◽  
A. S. Perlin
Keyword(s):  
Hydrogen Atom ◽  
Isotope Effect ◽  
Galactose Oxidase ◽  
Relative Impact ◽  
Chemical Transformations ◽  
Product Analysis ◽  
Deuterium Isotope Effect ◽  
Oxidation Rates ◽  
Selective Chemical ◽  
Sugar Derivatives

The stereochemistry of dehydrogenation of the primary carbinol group of D-galactose by D-galactose oxidase has been determined. Using D-galactose-6-d and methyl β-D-galactopyranoside-6-d, it has been established that the reaction involves removal of the pro-S 6-hydrogen atom. This conclusion is based on product analysis, and on the relative impact of the deuterium isotope effect on oxidation rates of substrates having different R:S deuteration patterns. The absolute configurations at C-6 of these substrates have been determined by selective chemical transformations to products of known configuration. The rotational conformation of the 6-carbinol group of D-galactose and its possible relationship to the specificity of the enzyme are discussed, as well as the stereochemistry of reductive deuteration of aldehydo sugar derivatives.

Correlation of isotope effects in substitution reactions with nucleophilicities. Secondary α-deuterium isotope effect in the iodide-131 exchange of methyl-d3 iodide

1967 ◽  
Vol 45 (18) ◽  
pp. 2023-2031 ◽  
Author(s):  
Stanley Seltzer ◽  
Andreas A. Zavitsas
Keyword(s):  
Nucleophilic Substitution ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Substitution Reactions ◽  
Deuterium Isotope Effect ◽  
Nucleophilic Substitution Reactions ◽  
Leaving Group ◽  
The Difference

The secondary α-deuterium isotope effect in iodide-131 exchange of methyl-d3 iodide is kH/kD = 1.05 ± 0.01 in methanol and 1.10 ± 0.04 in water at 20°. A correlation of secondary α-deuterium and 13C effects, in bimolecular nucleophilic substitution reactions, with the difference of E values between nucleophile and leaving group is presented.

The photodissociation of ammonia in the absorption system. Part I. Deuterium isotope effects in the photodissociation

1977 ◽  
Vol 55 (8) ◽  
pp. 1380-1386 ◽  
Author(s):  
S. Koda ◽  
R. A. Back
Keyword(s):  
Hydrogen Atom ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Quantum Yields ◽  
Absorption System ◽  
System Part ◽  
Deuterium Isotope Effects

The photolyses of mixtures of NH3, NH2D, NHD2, and ND3 have been studied at wave lengths of 2144, 2139, 2062, and 1850 Å in the presence of C3H8 as a hydrogen atom scavenger. Quantum yields of dissociation have the same values for all four species, presumably unity. Analysis of the H2 and HD produced permitted evaluation of intramolecular deuterium isotope effects in the photodissociation of NH2D and ND2H. At the two shortest wavelengths dissociation of H was favored by a factor of 2 or 3, while at 2144 and 2139 Å the isotope effect was much larger. Implications for the mechanism of the predissociation of the Ã-state of ammonia are discussed briefly. The system does not appear to be useful for the photochemical separation of deuterium.

Réactions d'addition nucléophiles sur les cétones. Mise en évidence d'un effet directionnel d'origine stérique dans l'effet isotopique secondaire du deutérium

1980 ◽  
Vol 58 (1) ◽  
pp. 55-59 ◽  
Author(s):  
Bernard Boyer ◽  
Gérard Lamaty ◽  
Jean-Pierre Roque ◽  
Patrick Geneste
Keyword(s):  
Kinetic Study ◽  
Isotope Effect ◽  
Carbonyl Compounds ◽  
Isotope Effects ◽  
Reaction Process ◽  
Addition Reactions ◽  
Deuterium Isotope Effect ◽  
Directional Effect ◽  
Sulfite Ions ◽  
Process Journal

A kinetic study of the addition reactions of borohydride and sulfite ions and of hydroxylamine to a number of stereospecifically deuterated carbonyl compounds (3,3,5,5-tetramethyl cyclohexanone, 7,7-d2-bicyclo[2,2,1]-2-bornanone) leads to the observation of a distant secondary deuterium isotope effect. The results obtained reveal the intervention of a directional effect in the steric origin of these isotope effects. In particular, this study shows the importance of the orientation of the vibrations brought into play by a C—D bond during the reaction process. (Journal translation)

DEUTERIUM KINETIC ISOTOPE EFFECTS: V TEMPERATURE DEPENDENCE OF β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ISOPROPYL COMPOUNDS

1961 ◽  
Vol 39 (10) ◽  
pp. 1989-1994 ◽  
Author(s):  
K. T. Leffek ◽  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Kinetic Isotope Effects ◽  
Methyl Groups ◽  
Deuterium Isotope Effect ◽  
Point Energy ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation

The secondary β-deuterium isotope effect (kH/kD) has been measured over a range of temperature for the water solvolysis reactions of isopropyl methanesulphonate, p-toluenesulphonate, and bromide. In these cases the isotope effect is due to a difference in entropies of activation of the isotopic analogues rather than a difference in the enthalpies of activation. It is suggested that the observed isotope effect is due to internal rotational effects of the methyl groups in the isopropyl radical, and the lack of an isotope effect on the enthalpy of activation is accounted for by a cancellation of an effect from this source and one from zero-point energy.

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.

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