Rate constants for the self-reactions of n- and sec-butylperoxy radicals and cyclohexylperoxy radicals. The deuterium isotope effect in the termination of secondary peroxy radicals

1968 ◽  
Vol 90 (4) ◽  
pp. 1058-1059 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
The Self ◽  
Peroxy Radicals ◽  
Deuterium Isotope Effect

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.

Absolute rate constants for hydrocarbon autoxidation. VI. Alkyl aromatic and olefinic hydrocarbons

1967 ◽  
Vol 45 (8) ◽  
pp. 793-802 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Steric Hindrance ◽  
Rate Constants ◽  
Peroxy Radical ◽  
Electron System ◽  
Chain Termination ◽  
The Self ◽  
Hydrogen Atom Abstraction ◽  
Peroxy Radicals ◽  
Absolute Rate

Absolute rate constants have been measured for the autoxidation of a large number of hydrocarbons at 30 °C. The chain-propagating and chain-terminating rate constants depend on the structure of the hydrocarbon and also on the structure of the chain-carrying peroxy radical. With certain notable exceptions which are mainly due to steric hindrance, the rate constants for hydrogen-atom abstraction increase in the order primary < secondary < tertiary; and, for compounds losing a secondary hydrogen atom, the rate constants increase in the order unactivated < acyclic activated by a single π-electron system < cyclic activated by a single Π-system < acyclic activated by two π-systems < cyclic activated by two π-systems. The rate constants for chain termination by the self-reaction of two peroxy radicals generally increase in the order tertiary peroxy radicals < acyclic allylic secondary  [Formula: see text] cyclic secondary  [Formula: see text] acyclic benzylic secondary < primary peroxy radicals < hydroperoxy radicals.

THE INHIBITED AUTOXIDATION OF STYRENE: PART I.THE DEUTERIUM ISOTOPE EFFECT FOR INHIBITION BY 2,6-DI-tert-BUTYL-4-METHYLPHENOL

1962 ◽  
Vol 40 (9) ◽  
pp. 1851-1864 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Isotope Effect ◽  
Rate Constants ◽  
Activation Energies ◽  
Deuterium Isotope Effect ◽  
Apparent Absence ◽  
Elementary Reactions ◽  
Tert Butyl ◽  
Rapid Exchange ◽  
Phenolic Inhibitor

Most previous work on the inhibition of autoxidation by phenols has indicated that the reaction involves abstraction of the phenolic hydrogen. However, the apparent absence of any appreciable deuterium isotope effect made it difficult to believe that abstraction could be rate controlling. The present work using styrene as the substrate, 2,6-di-tert-butyl-4-methyl-phenol as the inhibitor, and azo-bis-isobutyronitrile as the initiator has shown that this reaction has an unexpectedly large isotope effect, e.g. ~10.6 at 65 °C. Previous failures to detect an isotope effect are attributed to the rapid exchange of deuterium which takes place between deuterated phenols and traces of moisture or other hydroxyl-containing compounds present in the substrate. Rate constants and activation energies for some of the elementary reactions in the inhibited and uninhibited oxidation of styrene have been measured. It is suggested that a compound which functions in the same way as a weak phenolic inhibitor is formed in the apparently uninhibited oxidation.

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.

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.

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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