scholarly journals Isotope effect in the formation of H<sub>2</sub> from H<sub>2</sub>CO studied at the atmospheric simulation chamber SAPHIR

2010 ◽  
Vol 10 (12) ◽  
pp. 5343-5357 ◽  
Author(s):  
T. Röckmann ◽  
S. Walter ◽  
B. Bohn ◽  
R. Wegener ◽  
H. Spahn ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Isotope Effect ◽  
Surface Pressure ◽  
Kinetic Isotope Effect ◽  
Relative Rate ◽  
Isotope Effects ◽  
Ambient Conditions ◽  
Kinetic Isotope ◽  
Molecular Channel ◽  
Simulation Chamber

Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in the SAPHIR atmosphere simulation chamber under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only an indirect effect and cannot be effectively constrained. The molecular channel kinetic isotope effect KIEmol, the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) at surface pressure, is determined to be KIEmol=1.63−0.046+0.038. This is similar to the kinetic isotope effect for the total removal of HCHO from a recent relative rate experiment (KIEtot=1.58±0.03), which indicates that the KIEs in the molecular and radical photolysis channels at surface pressure (≈100 kPa) may not be as different as described previously in the literature.

scholarly journals Isotope effect in the formation of H<sub>2</sub> from H<sub>2</sub>CO studied at the atmospheric simulation chamber SAPHIR

2009 ◽  
Vol 9 (6) ◽  
pp. 25187-25212 ◽  
Author(s):  
T. Röckmann ◽  
S. Walter ◽  
B. Bohn ◽  
R. Wegener ◽  
H. Spahn ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Isotope Effect ◽  
Relative Rate ◽  
Isotope Effects ◽  
Order Effect ◽  
Ambient Conditions ◽  
Kinetic Isotope ◽  
Photolysis Frequencies ◽  
Rate Experiment ◽  
Molecular Channel

Abstract. Formaldehyde of known, near-natural isotopic composition was photolyzed in a large photochemical reactor under ambient conditions. The isotopic composition of the product H2 was used to determine the isotope effects in formaldehyde photolysis. The experiments are sensitive to the molecular photolysis channel, and the radical channel has only a second order effect and can thus not be derived with high precision. The molecular channel kinetic isotope effect (KIEmol), the ratio of photolysis frequencies j(HCHO→CO+H2)/j(HCDO→CO+HD) under tropospheric conditions is determined to be KIEmol=1.63±0.03. Combining this result with the total KIE from a recent relative rate experiment, it is likely that KIEmol and KIErad are not as different as described previously in the literature.

SOME DEUTERIUM KINETIC ISOTOPE EFFECTS: IV. β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ETHYL, ISOPROPYL, AND tert-BUTYL COMPOUNDS

1960 ◽  
Vol 38 (11) ◽  
pp. 2171-2177 ◽  
Author(s):  
K. T. Leffek ◽  
J. A. Llewellyn ◽  
R. E. Robertson
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
Tert Butyl ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Intramolecular Forces

The secondary β-deuterium isotope effects have been measured in the water solvolytic reaction of alkyl halides and sulphonates for primary, secondary, and tertiary species. In every case the kinetic isotope effect was greater than unity (kH/kD > 1). This isotope effect may be associated with varying degrees of hyperconjugation or altered non-bonding intramolecular forces. The experiments make it difficult to decide which effect is most important.

Solvolysis of specifically deuterated 7-chloro- and 7-bromo-exo-2-norbornyl brosylates; unusually large γ-kinetic isotope effects in the absence of σ-participation

1980 ◽  
Vol 58 (16) ◽  
pp. 1738-1750 ◽  
Author(s):  
Nick Henry Werstiuk ◽  
George Timmins ◽  
Frank Peter Cappelli
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Kinetic Isotope

A series of specifically deuterated syn-7-chloro-, anti-7-chloro-, syn-7-bromo-, and anti-7-bromo-exo-2-norbornyl brosylates have been prepared and solvolyzed in NaOAc-buffered 80:20 EtOH–H2O. For solvolysis at 25 °C the γ-kinetic isotope effects (KIE's) for syn-7-chloro-exo-2-norbornyl brosylate-endo-6-d (1e), anti-7-chloro-exo-2-norbornyl brosylate-endo-6-d (2c), syn-7-bromo-exo-2-norbornyl brosylate-endo-6-d (1f), anti-7-bromo-exo-2-norbornyl brosylate-endo-6-d (2d), syn-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (1g), anti-7-chloro-exo-2-norbornyl brosylate-exo,exo-5,6-d2 (2e) are 1.125 ± 0.007, 1.128 ± 0.005, 1.063 ± 0.008, 1.149 ± 0.020, 1.119 ± 0.011, and 1.115 ± 0.013, respectively. There is no detectable γ-kinetic isotope effect for solvolysis of anti-7-chloro-endo-2-norbornyl brosylate-endo-6-d(3a) and the β-KIE for anti-7-chloro-exo-2-norbornyl brosylate-exo-3-d(4a) is 1.111 ± 0.011. From a consideration of the possible sources of the unusually large secondary KIE's, we conclude that the exo-6-d and endo-6-d γ-KIE's likely are derived from a combination of effects rather than from participation of the C1—C6 bond in the ionization step.

Arrhenius-Parameter und kinetischer Isotopeneffekt für die Reaktion von Wasserstoffatomen mit Silan

1974 ◽  
Vol 29 (3) ◽  
pp. 493-496 ◽  
Author(s):  
Peter Potzinger ◽  
Louis C. Glasgow ◽  
Bruno Reimann
Keyword(s):  
Kinetic Isotope Effect ◽  
Relative Rate ◽  
Isotope Effects ◽  
Preexponential Factor ◽  
Kinetic Isotope Effects ◽  
Hydrogen Atoms ◽  
Kinetic Isotope ◽  
Abstraction Reaction ◽  
Upper Limits ◽  
Relative Rate Constants

The Reaction of Hydrogen Atoms with Silane; Arrhenius Parameters and Kinetic Isotope Effect Relative rate constants were measured for the systems H + C2H4/SiD4 and D + C2D4/SiH4 over a wide temperature range. From the known arrheniusparameter for the reaction H + C2H4 the activation energy EA and the preexponential factor A of the abstraction reactionH + SiD4 → HD + SiD3may be calculated. Values of EA = 3.2 kcal/Mol and A = 4.92 • 1013 cm3 Mol-1 sec-1 were obtained. Upper limits for the kinetic isotope effects are given in the paper

scholarly journals Pressure dependence of the deuterium isotope effect in the photolysis of formaldehyde by ultraviolet light

2010 ◽  
Vol 10 (7) ◽  
pp. 3455-3462 ◽  
Author(s):  
E. J. K. Nilsson ◽  
V. F. Andersen ◽  
H. Skov ◽  
M. S. Johnson
Keyword(s):  
Isotope Effect ◽  
Pressure Dependence ◽  
Kinetic Isotope Effect ◽  
Ambient Pressure ◽  
Deuterium Isotope Effect ◽  
Kinetic Isotope ◽  
Molecular Channel ◽  
The University ◽  
First Time ◽  
Gas Pressures

Abstract. The pressure dependence of the relative photolysis rate of HCHO vs. HCDO has been investigated for the first time, using a photochemical reactor at the University of Copenhagen. The dissociation of HCHO vs. HCDO using a UVA lamp was measured at total bath gas pressures of 50, 200, 400, 600 and 1030 mbar. The products of formaldehyde photodissociation are either H2 + CO (molecular channel) or HCO + H (radical channel), and a photolysis lamp was chosen to emit light at wavelengths that greatly favor the molecular channel. The isotope effect in the dissociation, kHCHO/kHCDO, was found to depend strongly on pressure, varying from 1.1 + 0.15/−0.1 at 50 mbar to 1.75±0.10 at 1030 mbar. The results can be corrected for radical channel contribution to yield the kinetic isotope effect for the molecular channel; i.e. the KIE in the production of molecular hydrogen. This is done and the results at 1030 mbar are discussed in relation to previous studies at ambient pressure. In the atmosphere the relative importance of the two product channels changes with altitude as a result of changes in pressure and actinic flux. The study demonstrates that the δD of photochemical hydrogen produced from formaldehyde will increase substantially as pressure decreases.

scholarly journals Insights Into the Known 13C Depletion of Methane—Contribution of the Kinetic Isotope Effects on the Serine Hydroxymethyltransferase Reaction

2022 ◽  
Vol 9 ◽  
Author(s):  
Gerd Gleixner
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Serine Hydroxymethyltransferase ◽  
Chemical Degradation ◽  
Methyl Groups ◽  
Kinetic Isotope ◽  
Isotopic Pattern ◽  
Before And After ◽  
Metal Organic

We determined the kinetic isotope effect on the serine hydroxymethyltransferase reaction (SHMT), which provides important C1 metabolites that are essential for the biosynthesis of DNA bases, O-methyl groups of lignin and methane. An isotope effect on the SHMT reaction was suggested being responsible for the well-known isotopic depletion of methane. Using the cytosolic SHMT from pig liver, we measured the natural carbon isotope ratios of both atoms involved in the bond splitting by chemical degradation of the remaining serine before and after partial turnover. The kinetic isotope effect 13(VMax/Km) was 0.994 0.006 and 0.995 0.007 on position C-3 and C-2, respectively. The results indicated that the SHMT reaction does not contribute to the 13C depletion observed for methyl groups in natural products and methane. However, from the isotopic pattern of caffeine, isotope effects on the methionine synthetase reaction and on reactions forming Grignard compounds, the involved formation and fission of metal organic bonds are likely responsible for the observed general depletion of “activated” methyl groups. As metal organic bond formations in methyl transferases are also rate limiting in the formation of methane, they may likely be the origin of the known 13C depletion in methane.

ISOTOPE EFFECTS IN MIXTURES OF LIQUID H2O AND T2O

1966 ◽  
Vol 44 (6) ◽  
pp. 689-694 ◽  
Author(s):  
Mark Salomon
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Hydroxide Ion ◽  
Kinetic Isotope ◽  
Hydronium Ion ◽  
Mercury Cathode

Calculations are presented for the equilibrium tritium isotope effect involving water, hydronium ion, and hydroxide ion. The results are used to predict the kinetic isotope effect in the transfer of protons to a mercury cathode.

Kinetic evidence for the importance of solvent-separated ion pairs during the solvolyses of adamantylideneadamantyl derivatives

2004 ◽  
Vol 82 (9) ◽  
pp. 1336-1340
Author(s):  
Xicai Huang ◽  
Andrew J Bennet
Keyword(s):  
Ionic Strength ◽  
Transition State ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Ion Pairs ◽  
Kinetic Isotope Effects ◽  
Ion Pair ◽  
Salt Effects ◽  
Kinetic Isotope

The aqueous ethanolysis reactions of adamantylideneadamantyl tosylate, -bromide, and -iodide (1-OTs, 1-Br and 1-I) were monitored as a function of ionic strength. Special salt effects are observed during the solvolyses of both homoallylic halides, but not in the case of the tosylate 1-OTs. The measured α-secondary deuterium kinetic isotope effects for the solvolysis of 1-Br in 80:20 and 60:40 v/v ethanol–water mixtures at 25 °C are 1.110 ± 0.018 and 1.146 ± 0.009, respectively. The above results are consistent with the homoallylic halides reacting via a virtual transition state in which both formation and dissociation of a solvent-separated ion pair are partially rate-determining. While the corresponding transition state for adamantylideneadamantyl tosylate involves formation of the solvent-separated ion pair.Key words: salt effects, kinetic isotope effect, internal return, solvolysis, ion pairs.

scholarly journals Kinetic isotope effects for fast deuterium and proton exchange rates

2016 ◽  
Vol 18 (15) ◽  
pp. 10144-10151 ◽  
Author(s):  
Estel Canet ◽  
Daniele Mammoli ◽  
Pavel Kadeřávek ◽  
Philippe Pelupessy ◽  
Geoffrey Bodenhausen
Keyword(s):  
Exchange Rates ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Proton Exchange ◽  
Kinetic Isotope ◽  
Spin Pairs

By monitoring the effect of deuterium decoupling on the decay of transverse 15N magnetization in D–15N spin pairs during multiple-refocusing echo sequences, we have determined fast D–D exchange rates kD and compared them with fast H–H exchange rates kH in tryptophan to determine the kinetic isotope effect as a function of pH and temperature.

Sign in / Sign up

Export Citation Format

Share Document