SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: I. DEUTERIUM EFFECTS IN THE BUNTE SALT REACTION

1964 ◽  
Vol 42 (4) ◽  
pp. 851-855 ◽  
Author(s):  
K. T. Leffek
Keyword(s):  
Aqueous Ethanol ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Sodium Thiosulphate ◽  
Deuterium Isotope Effect ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Rate Ratios ◽  
Aqueous Ethanol Solvent

The secondary deuterium isotope effects have been measured for the reaction between sodium thiosulphate and α-deuterated methyl, ethyl, and n-propyl bromide, and also for β- and γ-deuterated n-propyl bromide, in aqueous ethanol solvent. The α-deuterium isotopic rate ratios (kH/kD) are all greater than unity. These unexpected results are discussed with respect to the suggested use of the α-deuterium isotope effect as a test of mechanism in nucleophilic substitutions.

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. VI. Effect of α and β Deuteration of Alkyl Halides in their Menschutkin Reactions with Pyridine in Nitrobenzene

1972 ◽  
Vol 50 (7) ◽  
pp. 986-991 ◽  
Author(s):  
K. T. Leffek ◽  
A. F. Matheson
Keyword(s):  
Isotope Effects ◽  
Side Reaction ◽  
Kinetic Isotope Effects ◽  
Alkyl Halides ◽  
State Structure ◽  
Transition State Structure ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
Rate Ratios

A survey of kinetic, secondary deuterium isotope effects, for α, β, and γ deuterated alkyl halides reacting with pyridine in nitrobenzene solvent has been made. α-Deuterium effects have been measured for eight compounds, β-deuterium effects for four compounds, and one rate ratio for γ-deuteration is reported. The possible errors in the rate ratios for β-deuterated compounds, resulting from the elimination side reaction have been determined. The results are discussed in terms of transition state structure.

Secondary Kinetic Isotope Effects in Bimolecular Nucleophilic Substitutions. V. The Role of the Solvent in the Reaction Between Methyl Iodide and Pyridine

1972 ◽  
Vol 50 (7) ◽  
pp. 982-985 ◽  
Author(s):  
K. T. Leffek ◽  
A. F. Matheson
Keyword(s):  
Transition State ◽  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
State Structure ◽  
Transition State Structure ◽  
Initial State ◽  
Nucleophilic Substitutions ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects

Secondary kinetic deuterium isotope effects are presented for the reaction of methyl-d3 iodide and pyridine in four different solvents. Calculations on mass and moment of inertia change with deuteration in the initial state and an assumed tetrahedral transition state, together with internal rotational effects, are used to rationalize the inverse isotope effects. It is concluded from the variation of the isotopic rate ratio, that the transition state structure varies with solvent.

SECONDARY KINETIC ISOTOPE EFFECTS IN BIMOLECULAR NUCLEOPHILIC SUBSTITUTIONS: II. α-DEUTERIUM EFFECTS IN MENSCHUTKIN REACTIONS OF METHYL IODIDE

1965 ◽  
Vol 43 (1) ◽  
pp. 40-46 ◽  
Author(s):  
K. T. Leffek ◽  
J. W. MacLean
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Systematic Change ◽  
Tertiary Amines ◽  
Nucleophilic Substitutions ◽  
Methyl Group ◽  
Kinetic Isotope ◽  
Deuterium Substitution ◽  
Different Temperatures ◽  
Rate Ratios

Secondary deuterium isotope effects have been measured for the reactions between methyl and methyl-d3 iodides and a series of tertiary amines in benzene solvent. Deuterium substitution increased the rate of each reaction but the rate ratios (kH/kD) show no systematic change with variation in the structure of the amine. The isotope effect for the reaction with 2-picoline was measured at different temperatures over a range of 40 deg and shows no change. These isotope effects may be rationalized as internal rotational effects of the methyl group or as solvation effects.

scholarly journals Secondary kinetic isotope effects in bimolecular nucleophilic substitutions. III. Deuterium effects in the Bunte salt reaction of methyl halides and sulfonates

1969 ◽  
Vol 47 (9) ◽  
pp. 1537-1541 ◽  
Author(s):  
G. E. Jackson ◽  
K. T. Leffek
Keyword(s):  
Isotope Effects ◽  
Activation Parameters ◽  
Kinetic Isotope Effects ◽  
Conductivity Measurements ◽  
Nucleophilic Substitutions ◽  
Reaction Conditions ◽  
Methyl Halides ◽  
Kinetic Isotope ◽  
Deuterium Isotope Effects ◽  
The Difference

Secondary kinetic deuterium isotope effects have been measured for the reaction between thiosulfate ion and methyl-d3 halides and sulfonates in 50% v/v ethanol–water. The results are used to extend the correlation of Seltzer of kH/kD with the difference between the polarizabilities of the attacking nucleophile and the leaving group.Dissociation constants for the [NaS2O3]− ion have been determined by conductivity measurements for the reaction conditions and used to calculate the concentration of free thiosulfate ions present in the reaction mixture. The activation parameters ΔH≠ and ΔS≠, based on second order rate constants calculated with respect to the concentration of thiosulfate ion, are reported.

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.

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 Kinetic isotope effects of peptidylglycine α-hydroxylating mono-oxygenase reaction

1998 ◽  
Vol 336 (1) ◽  
pp. 131-137 ◽  
Author(s):  
Kenichi TAKAHASHI ◽  
Tetsuo ONAMI ◽  
Masato NOGUCHI
Keyword(s):  
Isotope Effects ◽  
Kinetic Isotope Effects ◽  
Tracer Method ◽  
Deuterium Isotope Effect ◽  
Critical Determinant ◽  
Product Release ◽  
Kinetic Isotope ◽  
Hydroxylation Reaction ◽  
Double Label ◽  
Rate Limiting

Many bioactive polypeptides or neuropeptides possess a C-terminal α-amide group as a critical determinant for their optimal bioactivities. The amide functions are introduced by the sequential actions of peptidylglycine α-hydroxylating mono-oxygenase (PHM; EC 1.14.17.3) and peptidylamidoglycollate lyase (PAL; EC 4.3.2.5) from their glycine-extended precursors. In the present study we examined the kinetic isotope effects of the frog PHM reaction by competitive and non-competitive approaches. In the competitive approach we employed the double-label tracer method with d-Tyr-[U-14C]Val-Gly, d-Tyr-[3,4-3H]Val-[2,2-2H2]-Gly, and d-Tyr-Val-(R,S)[2-3H]Gly as substrates, and we determined the deuterium and tritium effects on Vmax/Km as 1.625±0.041 (mean±S.D.) and 2.71±0.16 (mean±S.D.), respectively. The intrinsic deuterium isotope effect (Dk) on the glycine hydroxylation reaction was estimated to be 6.5–10.0 (mean 8.1) by the method of Northrop [Northrop (1975) Biochemistry 14, 2644–2651]. In the non-competitive approach with N,N-dimethyl-1,4-phenylenediamine as a reductant, however, the deuterium effect on Vmax (DV) was approximately unity, although the deuterium effect on Vmax/Km (DV/K) was comparable to that obtained by the competitive approach. These results indicated that DV was completely masked by the presence of one or more steps much slower than the glycine hydroxylation step and that DV/K was diminished from Dk by a large forward commitment to catalysis. The addition of PAL, however, increased the apparent DV from 1.0 to 1.2, implying that the product release step was greatly accelerated by PAL. These results suggest that the product release is rate-limiting in the overall PHM reaction. The large Dk indicated that the glycine hydroxylation catalysed by PHM might proceed in a stepwise mechanism similar to that proposed for the dopamine β-hydroxylase reaction [Miller and Klinman (1983) Biochemistry 22, 3091–3096].

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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