SOME DEUTERIUM ISOTOPE EFFECTS: I. WATER SOLVOLYSIS OF METHYL-d3 ESTERS

1960 ◽  
Vol 38 (2) ◽  
pp. 222-232 ◽  
Author(s):  
J. A. Llewellyn ◽  
R. E. Robertson ◽  
J. M. W. Scott
Keyword(s):  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Hydrogen Atoms ◽  
Deuterium Isotope Effect ◽  
Methyl Group ◽  
Out Of Plane ◽  
Thermodynamic Effects ◽  
Inverse Isotope Effect ◽  
Activated Complex

The α-deuterium isotope effect has been examined for the solvolysis of a series of esters containing a fully deuterated methyl group. The possible sources of the effect have been divided into "thermodynamic" effects which appear to favor more rapid reaction of the protium compound and "zero point" effects where stiffening of out-of-plane vibrations may account for the direction of the observed isotope effects. It appears that the inverse isotope effect may be a measure of the spatial restrictions placed on the hydrogen atoms on the carbon atom in the activated complex.

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.

scholarly journals Theory of Isotope Effect in YBaCuO

2011 ◽  
Vol 2011 ◽  
pp. 1-5
Author(s):  
Fu-sui Liu
Keyword(s):  
Oxygen Isotope ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Number Density ◽  
Doping Dependence ◽  
Local Spin ◽  
Inverse Isotope Effect

This paper is the first to demonstrate that a pure nonphonon mechanism can quantitatively explain all isotope effect experiments in YBaCuO (YBCO) and to conclude that the influence of zero-point oscillation on the two local spin-mediated interaction (TLSMI) causes the isotope effects in YBCO. This paper is the first to calculate the doping dependence of exponents of oxygen isotope effect for all quantities of YBCO, such as , T, pseudogap at , gap at 0 K, and number density of supercurrent carriers at 0 K. This paper points out that the observed inverse isotope effect of comes also from zero-point oscillation.

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.

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 photodissociation of ammonia in the absorption system. Part II. Translational excitation of the hydrogen atoms produced, and the mechanism of the predissociation

1977 ◽  
Vol 55 (8) ◽  
pp. 1387-1395 ◽  
Author(s):  
R. A. Back ◽  
S. Koda
Keyword(s):  
Isotope Effects ◽  
Quantum Yields ◽  
Translational Energy ◽  
Molecular Dissociation ◽  
Hydrogen Atoms ◽  
Bending Vibration ◽  
Upper Limits ◽  
Out Of Plane ◽  
System Part ◽  
Correlation Rules

The photolyses of NH3 and ND3 have been studied at 2139, 2062, and 1850 Å in the presence of propane and ethylene. Upper limits (none was actually observed) were established for the quantum yields of molecular dissociation of D2 from ND3 of 0.003 and 0.004 at 2139 and 2062 Å, while at 1850 Å a definite yield of 0.009 was obtained. Similar results were observed with NH3. From the dependence of hydrogen yields on the ratio of ethylene to propane, it was concluded that H and D atoms were produced in the photolysis with excess translational energy. Values of the integrated reaction probability (IRP) of hot H atoms with propane were estimated to be 0.078, 0.070, and 0.045 at 2139, 2062, and 1850 Å respectively, while corresponding values for hot D atoms from ND3 were 0.083, 0.062, and 0.029. Implications of the decrease in IRP with increasing photon energy are discussed, and it is concluded that at the shorter wavelengths a second dissociation channel leading to NH2(2A1) becomes important. A mechanism for the predissociation of the Ã-state of ammonia is presented which accounts for this behaviour and for the deuterium isotope effects observed previously. It is suggested that the dissociation does not follow the state correlation rules for dissociation in the plane of the molecule, at least when the ν2 out-of-plane bending vibration in the Ã-state is excited to levels of υ2 = 2 or higher.

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.

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)

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.

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