Isotope Effects In Reactions Research Articles

Temperature dependences of hydrogen kinetic isotope effect in reactions of cyclohexane with Mn(VII), Cr(VI) and NO 2 + in solutions

Temperature dependences of hydrogen kinetic isotope effect (KIE) in reactions of cyclohexane with Mn(VII), Cr(VI) and NO 2 + in solutions have been studied. With increasing temperature from −10° to 140°C, KIE decreases and the equation kH/kD=AH/ADexp(ΔE/RT) is met.

Extensions of the Melander–Westheimer Postulate: Isotope Effects in Reactions with Equilibrium Values Far from Unity

AbstractThe symmetric dependence of experimental primary kinetic isotope effects on the free energy change, obtained for reaction series with zero equilibrium isotope effects, can be inverted to obtain the free energy profile along the reaction coordinate. Trends in the kinetic isotope effects for the general case of non‐vanishing equilibrium effects can be understood by an extension of the same theory. Comparison is made with experiments for reactions of halogen atoms with hydrogen/deuterium molecules.

ChemInform Abstract: TEMPERATURE DEPENDENCE OF BROMINE KINETIC ISOTOPE EFFECTS FOR REACTIONS OF N‐BUTYL AND TERT‐BUTYL BROMIDES

Chemischer InformationsdienstVolume 11, Issue 28 Preparative Organic Chemistry ChemInform Abstract: TEMPERATURE DEPENDENCE OF BROMINE KINETIC ISOTOPE EFFECTS FOR REACTIONS OF N-BUTYL AND TERT-BUTYL BROMIDES J. F. WILLEY, J. F. WILLEYSearch for more papers by this authorJ. W. TAYLOR, J. W. TAYLORSearch for more papers by this author J. F. WILLEY, J. F. WILLEYSearch for more papers by this authorJ. W. TAYLOR, J. W. TAYLORSearch for more papers by this author First published: July 15, 1980 https://doi.org/10.1002/chin.198028113AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue28July 15, 1980 RelatedInformation

6] Use of secondary α-hydrogen isotope effects in reactions of pyrimidine nucleoside/nucleotide metabolism: Thymidylate synthetase

Publisher Summary This chapter discusses that secondary α-hydrogen isotope effects are useful tools that may aid in ascertaining whether an enzyme-catalyzed reaction or covalent interaction of an inhibitor with an enzyme involves rehybridization of a carbon atom of the ligand at or before the rate-determining step of the reaction. It reviews the catalytic mechanism of thymidylate (dTMP) synthetase, as well as the interaction of 5-fluoro-2'-deoxyuridylate (FdUMP) with this enzyme. A salient feature of this mechanism is that a primary event in catalysis involves addition of a nucleophile of the enzyme to the 6-position of the pyrimidine heterocycle to form transient 5, 6-dihydropyrimidine intermediates, in which the 6-carbon is rehybridized, from sp 2 to sp 3 . FdUMP behaves as a quasi-substrate for this reaction, proceeding through the first two steps of the mechanism. The chapter also reviews that kinetic studies indicate that initial attack of thiolate is probably rate determining in this reaction; if so, it may be concluded that the isotope effect observed here is the true kinetic isotope effect of the reaction rather than a pre-equilibrium isotope effect. However, from available evidence, it is not possible to determine whether rehybridization of the 6-carbon of BrdUMP in the enzymic reaction occurs at or before the rate-determining step of the reaction. Results demonstrate that secondary α- hydrogen isotope effects may be of great utility, in demonstrating the existence of transient 5, 6-dihydropyrimidine intermediates, in both chemical and enzymic reactions of pyrimidine nucleosides and nucleotides.

The importance of isotope-dependent transmission coefficients in calculating low-temperature isotope effects

We compare conclusions which may be drawn from our previous work (Truhlar et al. [5]), on the collinear H + H2 reaction concerning practical calculations of isotope effects with conclusions drawn by Wu et al. [1]. We present calculations designed to elucidate the differences in conclusions. We suggest that one should not assume that accurate isotope effects for reactions involving H and D can be calculated from transition state theory using transmission coefficients equal to unity, especially at room temperature and lower temperatures.

Aromatic hydrogen isotope effects in reactions of benzenediazonium salts

Aromatic hydrogen isotope effects in reactions of benzenediazonium salts

ChemInform Abstract: KINETIC ISOTOPE EFFECTS IN REACTIONS OF HOT METHYL RADICALS WITH HYDROGEN

Chemischer InformationsdienstVolume 4, Issue 46 Preparative Organic Chemistry ChemInform Abstract: KINETIC ISOTOPE EFFECTS IN REACTIONS OF HOT METHYL RADICALS WITH HYDROGEN CHENG-TEH TING, CHENG-TEH TINGSearch for more papers by this authorRALPH E. JUN. WESTON, RALPH E. JUN. WESTONSearch for more papers by this author CHENG-TEH TING, CHENG-TEH TINGSearch for more papers by this authorRALPH E. JUN. WESTON, RALPH E. JUN. WESTONSearch for more papers by this author First published: November 13, 1973 https://doi.org/10.1002/chin.197346128Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume4, Issue46November 13, 1973 RelatedInformation

Kinetic isotope effects in reactions of hot methyl radicals with hydrogen

ADVERTISEMENT RETURN TO ISSUEArticleNEXTKinetic isotope effects in reactions of hot methyl radicals with hydrogenCheng-Teh Ting and Ralph E. Weston Jr.Cite this: J. Phys. Chem. 1973, 77, 19, 2257–2266Publication Date (Print):September 1, 1973Publication History Published online1 May 2002Published inissue 1 September 1973https://doi.org/10.1021/j100638a001RIGHTS & PERMISSIONSArticle Views34Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts

Kinetic Isotope Effects in Reactions of Thiols with Radicals Formed by Radiolysis

A novel method is described for determining the kinetic isotope effect on the reaction in which a free radical abstracts a hydrogen atom from a H-donor such as a thiol, RSH. The radical is generated by gamma irradiation of an appropriate precursor, and the isotope effect is obtained by comparing the results of two experiments: in the first, the radical is allowed to react with tritiated RSH; in the second, the radical reacts with tritium-labeled RSD. The validity of this system was tested by generating the cyclohexyl radical in two different ways: radiolysis of cyclohexane and decomposition of the perester ${\rm C}_{6}{\rm H}_{5}-{\rm CO}_{2}-{\rm OC}_{4}{\rm H}_{9}-t$ . The $k_{{\rm H}}/k_{{\rm D}}$ ratios from these independent methods are in excellent agreement. The utility of the method was demonstrated by radiolyzing the ethyl ester of N,N-dimethylglycine. The isotope effect for abstraction of a hydrogen from thiols by the $({\rm CH}_{3})_{2}{\rm N}-...

Kinetic Isotope Effect Studies on the Reaction of Benzyl Nitrate with Base in Varions Solvents

The role of solvent and base on the nature of the transition state for the concerted one-step carbonyl elimination reaction of benzyl nitrate has been examined using rate and kinetic isotope effect techniques. The primary hydrogen–deuterium isotope effect was found to increase with increasing strength of the abstracting base, kH/kD = 5.94 and 6.41 at 30° for reaction with EtO−/EtOH and t-BuO−/t-BuOH, respectively. The nitrogen isotope effect decreased with increasing strength of the abstracting base, 2.07, 1.82, and 1.54% for reaction with OH−/40 vol % EtOH–H2O, EtO−/EtOH, and t-BuO−/t-BuOH, respectively. The conclusion is reached that an increase in the strength of the abstracting base leads to a more reactant-like transition state with decreased rupture of both the C—H and O—N bonds. The role of solvent on the nature of the transition state was examined by determining rates and nitrogen isotope effects for reaction in various ethanol–water and ethanol–dimethyl sulfoxide mixtures. The nitrogen effect was found to remain essentially constant in solvent mixtures ranging from 65 vol % EtOH–H2O on the one hand to 80 vol% EtOH–DMSO on the other hand where the rate constants differed by a factor of 100 fold. It is concluded that solvent plays only a very minor role in determining transition state structure for the concerted elimination reaction of a neutral substrate with base.

Comparison of isotope effects in reactions of monohydrosilanes

Comparison of isotope effects in reactions of monohydrosilanes

Monte Carlo Calculations of Energy Partitioning and Isotope Effects in Reactions of Fluorine Atoms with H2, HD, and D2

A total of 16 000 three-dimensional classical trajectories on an optimized semiempirical potential energy surface were computed for collisions of F atoms with H2, HD, and D2. Analysis of the reactive trajectories indicates general agreement with results of infrared chemiluminescence and chemical laser studies with respect to the partitioning of the available energy among the translational, rotational, and vibrational degrees of freedom in the reaction products. Of particular interest is the calculated effect of reactant rotation on the reaction cross sections for all the isotropic systems, and on the intramolecular isotope effect in the reaction of F with HD. These phenomena have not as yet been seen experimentally.

Deuterium solvent isotope effects in methanol solution. Part III. Proton transfer from 2-nitropropane and from 3-methyl-1-phenylbutyl phenyl ketone to methoxide ion

The extreme solvent isotope effects for the racemisation of D-(+)-3-methyl-1-phenylbutyl Phenyl ketone (α-phenyl-isocaprophenone)(kD/kH= 2·04) and the ionisation of 2-nitropropane (kD/kH= 2·28) have been measured for methanolic solutions of sodium methoxide at 25° C (where kD refers to MeOD as solvent). It is shown that the existence of large solvent isotope effects in reactions of this type implies a solvation number of 3 for the methoxide ion, if larger values are ruled out on structural grounds. Measurements in mixtures of MeOH and MeOD are interpreted in terms of the appropriately modified theory of solvent isotope effects and are shown to be consistent with a multiply solvated methoxide ion. The primary (substrate) isotope effect for the ionisation of 2-nitro[2-2H1]propane is found to have the value 7·4 in MeOH solution and ca. 6·9 in MeOD.

Preparation of deuteroglyoxylate and (A) DPND

Methods for the preparation of deuteroglyoxylate and (A) DPND are described. The two compounds are suitable for some investigations of kinetic isotope effects in reactions utilizing glyoxylate and DPN.

Secondary isotope effects in reactions catalyzed by yeast and muscle aldolase.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSecondary isotope effects in reactions catalyzed by yeast and muscle aldolaseJean F. Biellmann, E. L. O'Connell, and Irwin A. RoseCite this: J. Am. Chem. Soc. 1969, 91, 23, 6484–6488Publication Date (Print):November 1, 1969Publication History Published online1 May 2002Published inissue 1 November 1969https://doi.org/10.1021/ja01051a053RIGHTS & PERMISSIONSArticle Views54Altmetric-Citations22LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (648 KB) Get e-Alerts Get e-Alerts

The kinetics of the gas phase intramolecular elimination of isobutene from 2‐d1‐triisobutylaluminum and the deuterium isotope effect in reactions involving cyclic transition states

AbstractThe intramolecular elimination of isobutene from 2‐d1‐triisobutylaluminum has been studied in the gas phase for temperatures ranging between 102.4 and 184.6°C. The reaction is apparently homogeneous and obeys the first order rate law, yielding the following Arrhenius relationship: Excess ethylene was added to the starting material in order to avoid complications from the backreaction. The cyclic 4‐center nature of the transition state proposed earlier has been unequivocally demonstrated by deuterium labelling. Mass‐spectral analyses show that the isobutene formed contains no deuterium. The hydrolyses products of the mixed trialkylaluminum formed during the reaction consist of monodeuteroethane and 2‐d1‐isobutane. The observed negative entropy of activation of ∼12 cal/°‐mole agrees with prediction and implies a reasonably tight transition state structure. Combined with the corresponding data for the non deuterized Al(i‐bu)3 reported earlier, these data result in a primary kinetic deuterium isotope effect of kH/kD = 1.3 × 100.6/θ corresponding to a ratio of the isotopic rate constants of 3.7 at 25°C. This result is in excellent agreement with a predicted value of 1.4 × 100.7/θ and it is in line with literature data on similar reactions involving cyclic transition state complexes.

Deuterium solvent isotope effects in reactions catalyzed by isocitrate dehydrogenase

The result of substituting deuterium oxide for water on the rates of the overall and partial reactions catalyzed by the pig heart TPN-dependent isocitrate dehydrogenase has been studied. Although the overall oxidative decarboxylation of isocitrate proceeds 4.9 times as fast in H 2O as in D 2O, the rate of the separately measured oxalosuccinate decarboxylation reaction is only 1.4–1.7 times greater in water. In contrast, the oxalosuccinate reduction reaction proceeds 5.0 times faster in H 2O. These results suggest that dehydrogenation is the slow reaction in the oxidative decarboxylation of isocitrate and that a proton transfer is involved in this rate determining step.

Isotope effects in reactions of trifluoromethyl radicals with hydrogen chloride and hydrogen sulphide

Rate constants, Arrhenius parameters and primary kinetic isotope effects have been measured for the reactions of trifluoromethyl radicals with H2S, D2S, HCl and DCl: [graphic omitted] Quotients of A-factors do not differ significantly from unity, but values for (ED–EH) are significantly less than the respective zero-point-energy differences ΔE0 of 1.1 kcal mole–1. The reactivity of CF3 radicals towards the two substances is markedly less than that of CH3 radicals; the differences reside in the higher activation energies and may be attributed to the polar character of CF3.

Kinetic isotope effect in reaction between 4-nitrobenzyl-cyanide and ethoxide ion in ethanol + ether

The rate of the deuteron-transfer reaction between ethoxide ion and 4-nitrobenzylcyanide-α, α-d2 has been determined at six temperatures over the temperature range –40 to –90°. At the highest temperatures, the Arrhenius plot shows a negative deviation from linearity, and approaches that for the proton-transfer; this behaviour confirms the previous interpretation in terms of an unstable intermediate complex. At lower temperatures (–60 to –90°), the plot for the deuteron-transfer reaction is linear; the energy of activation is 1.85± 0.2 kcal mole–1 higher than for the proton-transfer, and the A-factor is about 5 times larger. These values can be interpreted in terms of tunnelling. On fitting the equations for a parabolic energy-barrier, with ΔH°= 0, we find for the height 10.3 kcal mole–1 and for the width 1.63 A. These are in good agreement with the values found independently from the non-linear Arrhenius plot for the proton-transfer reaction in the same medium (10.7 kcal mole–1 and 1.62 A).

Fall-off behaviour and kinetic isotope-effects in reactions of cyclic hydrocarbons

The geometrical and structural isomerizations of cyclopropane and the decomposition of cyclobutane are considered from the standpoint of the RRKM theory. The fall-off curves depend critically on the high-pressure Arrhenius parameters; the use of the latest values leads to good agreement with experiment in most cases. Whether or not a biradical mechanism is assumed, there is little effect on the calculated fall-off curves. The treatments are applied to isotope effects as functions of pressure and temperature. The activation energy difference ED–EH varies with pressure in a complicated way, a conclusion that throws light on apparent discrepancies between the results of different workers.