scholarly journals The influence of crown ethers on the kinetics of E1cB and E2 β-elimination reactions of di(4-nitrophenyl)fluoroethanes with sodium methoxide in methanol

1982 ◽  
Vol 60 (24) ◽  
pp. 3077-3080
Author(s):  
Kenneth T. Leffek ◽  
Grzegorz Schroeder
Keyword(s):  
Isotope Effect ◽  
Crown Ethers ◽  
Rate Constant ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Activation Parameters ◽  
Deuterium Isotope Effect ◽  
Kinetic Order ◽  
Elimination Reactions ◽  
Kinetics Of

The addition of crown ethers 1,4,7,10,13-pentaoxacyclopentadecane (15C5) and 1,4,7,10,13,16-hexaoxacyclooctadecane (18C6) in quantities equimolar to the base, to β-elimination reactions of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane and 1-fluoro-2,2-di(4-nitrophenyl)ethane promoted by sodium methoxide in methanol, has been investigated. In the E2 reaction of the monofluoro compound, the crown ethers caused no change in the kinetic order and only small changes in the second-order rate constants and activation parameters. The primary deuterium isotope effect was also unaltered by the presence of crown ethers.For the (E1cB)R reaction of the trifluoro compound, no change in kinetic order was found, but slightly larger rate constant changes and an increase in the isotope effect from kH/kD = 1.0 to 1.25 at 25 °C was observed. This is interpreted as an alteration in mechanism from (E1cB)R towards (E1cB)I.

Kinetics of the hydrolysis of thiochloroformate esters in pure water

1970 ◽  
Vol 48 (4) ◽  
pp. 522-527 ◽  
Author(s):  
A. Queen ◽  
T. A. Nour ◽  
M. N. Paddon-Row ◽  
K. Preston
Keyword(s):  
Isotope Effect ◽  
Structural Changes ◽  
Pure Water ◽  
Activation Parameters ◽  
Deuterium Isotope Effect ◽  
Hydro Carbon ◽  
Electron Donation ◽  
Kinetics Of ◽  
Hydrolysis Of

The effects of structural changes on the rates of hydrolysis of a series of thiochloroformate esters in water have been investigated. The reactivity is enhanced by increased electron donation by the hydro carbon group. These results, the activation parameters for the hydrolysis of methyl thiochloroformate and the solvent deuterium isotope effect, are shown to be consistent with the operation of the SN1 mechanism.

ABSOLUTE RATE CONSTANTS FOR HYDROCARBON AUTOXIDATION: III. α-METHYLSTYRENE, β-METHYLSTYRENE, AND INDENE

1966 ◽  
Vol 44 (10) ◽  
pp. 1113-1118 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
Propagation Rate ◽  
Absolute Rate ◽  
Order Process ◽  
Deuterium Isotope Effect ◽  
First Order ◽  
Process Rate Constant ◽  
Propagation Rate Constant

Absolute rate constants for the copolymerization of α-methylstyrene and oxygen have been measured from 13 to 50 °C. The propagation and termination rate constants can be represented by[Formula: see text]Experiments with 2,6-di-t-butyl-4-methylphenol at 65 °C have shown that C6H5C(CH3):CH2 and C6H5C(CD3):CD2 have the same propagation rate constant but that chain termination involves a deuterium isotope effect (kt)H/(kt)D ≈ 1.5.Absolute rate constants for the copolymerization of oxygen with β-methylstyrene and with indene at 30 °C showed that a significant fraction of the oxidation chains were terminated by a kinetically first order process (rate constant kx). The rate constants for β-methylstyrene and indene at 30 °C are kp = 51 and 142 l mole−1 s−1, kt = 1.6 × 107 and 2.5 × 107 l mole−1 s−1, and kx = 0.61 and 1.2 s−1, respectively. The propagation rate constant for indene can be separated into a rate constant for the copolymerization with oxygen (kadd = 128 l mole−1 s−1) and a rate constant for hydrogen atom abstraction (kabstr = 14 l mole−1 s−1). In the presence of heavy water the first order process for indene had a deuterium isotope effect (kx)/(kx)D2O ≈ 3.

Primary isotope effects and mechanism of base initiated β-elimination reactions of di-(p-nitrophenyl)fluoroethanes

1977 ◽  
Vol 55 (10) ◽  
pp. 1696-1700 ◽  
Author(s):  
Jan Kurzawa ◽  
Kenneth T. Leffek
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Second Order ◽  
Order Rate ◽  
Elimination Reactions

The second-order rate constants have been determined for the β-elimination reactions of 2,2-di-(p-nitrophenyl)-1,1,1-trifluoroethane, 2,2-di-(p-nitrophenyl)-1-fluoroethane, and their β-deuterated analogues with sodium methoxide in methanol. The primary isotope effects and activation parameters for these reactions are reported. It is suggested that the trifluoro-compound reacts via the pre-equilibrium carbanion mechanism (ElcB)R and that the monofluoro compound follows the E2 mechanism via a carbanion-like transition state.

Absolute rate constants for hydrocarbon autoxidation. XV. The induced decomposition of some t-hydroperoxides

1969 ◽  
Vol 47 (20) ◽  
pp. 3797-3801 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Rate Constants ◽  
The Self ◽  
Absolute Rate ◽  
Alkoxy Radical ◽  
Deuterium Isotope Effect ◽  
Alkoxy Radicals ◽  
Induced Decomposition ◽  
Alkylperoxy Radicals

The radical induced decomposition of several t-hydroperoxides at 30° has been studied. In the self reaction of t-alkylperoxy radicals the ratio of the rates of alkoxy radical diffusion from the cage to combination in the cage is essentially independent of the size of the t-alkyl group.The rate constant for abstraction from hydroperoxides of the hydroperoxidic hydrogen by alkoxy radicals is about 4 × 106 M−1 s−1 at 30°. This reaction has a deuterium isotope effect, kH/kD ≈ 5.The 1,1-diphenylethoxy radical undergoes a 1,2-phenyl shift to yield the 1-phenyl-1-phenoxyethyl radical more rapidly that it undergoes β-scission.

The reinvestigation of the kinetics of the reactions of fluorodi(4-nitrophenyl)ethanes with sodium methoxide in methanol

1982 ◽  
Vol 60 (13) ◽  
pp. 1696-1701 ◽  
Author(s):  
Kenneth T. Leffek ◽  
Grzegorz Schroeder
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Sodium Methoxide ◽  
Isotope Effects ◽  
Activation Parameters ◽  
Elimination Reaction ◽  
Methoxide Ion ◽  
Dimerization Reaction ◽  
Multistep Reaction ◽  
Kinetics Of

The procedure previously described for the preparation of 1-fluoro-2,2,-di(4-nitrophenyl)ethane actually yields 1,1,2-tri-(4-nitrophenyl)ethane. 1-Fluoro-2,2-di(4-nitrophenyl)ethane has been prepared and rate constants, isotope effects, and activation parameters for the β-elimination reaction with methoxide ion in methanol are reported. These parameters indicate a concerted E2 mechanism, with a fairly symmetrical transition state. The subsequent dimerization reaction of the olefin product to yield 1,1,3,3-tetra(4-nitrophenyl)butene-1 is described.The reaction of 1,1,1-trifluoro-2,2-di(4-nitrophenyl)ethane with methoxide ion in methanol has been reinvestigated and the reaction of the first product 1,1-difluoro-2,2-di(4-nitrophenyl)ethylene with excess methoxide, to give di(4-nitrophenyl)ketene dimethylacetal in a multistep reaction, is reported.

The kinetics and mechanisms of the gas phase pyrolyses of exo-2-norbornyl chloride and cyclopentyl chloride

1979 ◽  
Vol 57 (19) ◽  
pp. 2621-2625 ◽  
Author(s):  
J. L. Holmes ◽  
D. L. McGillivray ◽  
D. Yuan
Keyword(s):  
Gas Phase ◽  
Hydrogen Chloride ◽  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Temperature Range ◽  
Elimination Reactions ◽  
Chloride Elimination ◽  
Kinetics Of

The gas phase pyrolyses of exo-2-norbornyl chloride and cyclopentyl chloride were studied in the temperature range 570–670 K. The results obtained show that these compounds behave as typical secondary halides insofar as the kinetics of their hydrogen chloride elimination reactions are concerned. Labelling experiments showed that in the formation of both norbornene and cyclopentene, a cis-1,2 elimination with a deuterium isotope effect of ∼3 was involved. Nortricyclene also was produced from exo-2-norbornyl chloride, via a trans 1,3 elimination; this process is analogous to a fragmentation of the ionized molecule. No gas phase Wagner–Meerwein rearrangement was involved in the formation of either norbornene or nortricyclene.

Kinetics of Proton Transfer Reactions of Carbon Acids. IV. Primary Deuterium Isotope Effect in the Reaction of Di-(4-nitrophenyl)methane-d2 with t-Butoxide

1974 ◽  
Vol 52 (4) ◽  
pp. 592-596 ◽  
Author(s):  
Jae-Hang Kim ◽  
Kenneth T. Leffek
Keyword(s):  
Proton Transfer ◽  
Isotope Effect ◽  
Activation Parameters ◽  
Proton Transfer Reaction ◽  
Transfer Reactions ◽  
Deuterium Isotope Effect ◽  
Enthalpy Of Activation ◽  
Proton Transfer Reactions ◽  
Carbon Acids ◽  
Kinetics Of

The primary deuterium isotope effect has been measured for the proton transfer reaction from di-(4-nitrophenyl)methane to t-butoxide ion in a solvent consisting of 10% v/v toluene in t-butanol at a series of temperatures between 20 and 45 °C. The isotopic rate ratio, kH/kD, is 7.3 at 25 °C. The activation parameters showed an enthalpy of activation difference (ΔHD≠ − ΔHH≠) of only ca. [Formula: see text] kcal mol−1 and an entropy isotope effect (ΔSD≠ − ΔSH≠) of −2.4 cal mol−1 deg−1. The latter indicates, according to the theory of Bell, that tunnelling of the proton through the energy barrier is unimportant in this reaction. This result is compared to other reactions in the literature, in which tunnelling has been postulated to occur.

scholarly journals Substituent effect on lysozyme-catalysed hydrolysis of some β-aryl di-N-acetylchitobiosides

1969 ◽  
Vol 114 (3) ◽  
pp. 529-534 ◽  
Author(s):  
C. S. Tsai ◽  
J. Y. Tang ◽  
S. C. Subbarao
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Substituent Effect ◽  
Deuterium Isotope Effect ◽  
Catalytic Rate ◽  
Electron Donating Groups ◽  
First Time ◽  
Kinetics Of ◽  
Hydrolysis Of

Measurements are reported on the kinetics of the lysozyme-catalysed hydrolysis of several β-aryl di-N-acetylchitobiosides, some of which have been synthesized for the first time. The catalytic rate constants (kcat.) at 45° yield a curved Hammett plot (concave up) and the plot of ΔH‡ versus ΔS‡ has a sharp break. Substrates with electron-withdrawing groups exhibit a kinetic deuterium isotope effect (kHcat./kDcat.), whereas those with electron-donating groups show no such isotope effect. The results suggest the operation of different mechanisms for the two types of substrates.

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