ChemInform Abstract: Rates of Hydrogen Atom Abstraction from Benzyltrimethylsilanes by Bromine and tert-Butoxy Radical. The Question of the Stability of the α-(Trimethylsilyl)benzyl Radical.

ChemInform ◽  
1988 ◽  
Vol 19 (48) ◽  
Author(s):  
J. S. SWENTON ◽  
M. PLATZ ◽  
L. D. VENHAM
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Abstraction ◽  
Benzyl Radical ◽  
The Stability ◽  
Butoxy Radical

REACTIONS OF ALKOXY RADICALS: I. HYDROGEN ATOM ABSTRACTION FROM SUBSTITUTED TOLUENES

1966 ◽  
Vol 44 (20) ◽  
pp. 2381-2385 ◽  
Author(s):  
B. R. Kennedy ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Abstraction ◽  
High Electron ◽  
Hammett Equation ◽  
Alkoxy Radicals ◽  
Benzyl Radical ◽  
High Electron Affinity ◽  
Stabilizing Effect ◽  
Substituted Toluenes ◽  
Butoxy Radical

The relative rates of hydrogen atom abstraction from ten substituted toluenes by t-butoxy radicals in carbon tetrachloride at 40 °C have been measured and the data fitted to the Hammett equation. A much better correlation is obtained with the σ+ constants than with the σ constants of the substituents. In this respect, therefore, the reaction is similar to the majority of hydrogen atom abstraction reactions by radicals of moderate and high electron affinity. That is, the polar properties of the substituents are much more important than their stabilizing effect on the benzyl radical formed in the reaction.The cumyloxy radical has a similar reactivity to the t-butoxy radical. The p-nitrocumyloxy radical appears to be slightly more reactive and also slightly more susceptible to the polar effects of substituents than are t-butoxy or cumyloxy radicals.

Absolute rate constants for hydrocarbon oxidation. XI. The reactions of tertiary peroxy radicals

1968 ◽  
Vol 46 (16) ◽  
pp. 2655-2660 ◽  
Author(s):  
J. A. Howard ◽  
K. U. Ingold
Keyword(s):  
Hydrogen Atom ◽  
Rate Constants ◽  
Chain Termination ◽  
Hydrogen Atom Abstraction ◽  
Hydrocarbon Oxidation ◽  
Peroxy Radicals ◽  
Absolute Rate ◽  
Alkoxy Radical ◽  
Oxygen Chain ◽  
The Stability

Rate constants have been measured for the chain-terminating self-reactions of six tertiary peroxy radicals. The rate constants vary from ~ 1 × 103 M−1 s−1 for t-butylperoxy to ~ 6 × 104 M−1 s−1 for 1,1-diphenylethylperoxy radicals. It is suggested that the variation in the rate constants may be related to differences in the stability of the alkoxy radical products of tetroxide decomposition.Rate constants for hydrogen atom abstraction from aralkanes by tertiary peroxy radicals do not seem to be significantly affected by the structure of the attacking radical.In solution the triphenylmethylperoxy radical probably exists in equilibrium with the triphenylmethyl radical and oxygen. Chain termination in oxidations involving the triphenylmethylperoxy radical as the chain carrier occurs by the reaction of this radical with a triphenylmethyl radical.

Substituent effects on the stability and reactivity of norbornenyl and nortricyclyl radicals

1975 ◽  
Vol 28 (3) ◽  
pp. 639 ◽  
Author(s):  
TG Burrows ◽  
WR Jackson
Keyword(s):  
Hydrogen Atom ◽  
Substituent Effects ◽  
Starting Material ◽  
Hydrogen Atom Abstraction ◽  
Thioacetic Acid ◽  
Tributyltin Hydride ◽  
Hydride Reduction ◽  
The Stability

The products of addition of thioacetic acid to norbornadiene, and of tributyltin hydride and triphenyltin hydride reduction of exo-2-bromo- anti-7-thioacetoxynorborn-5-ene (7), and trans-5-bromo-3- thioacetoxynortricyclene (8), have been examined. In contrast to results obtained with the corresponding acetoxy compounds, the product ratios vary with the reducing reagent and the starting material and the ratio of (rate of rearrangement)/(rate of hydrogen atom abstraction) is significantly less for the thioacetoxy substituted radicals.

Reaction of Acyclic Hydrocarbons Towards t-Butoxy Radicals. A Study of Hydrogen Atom Abstraction by Using the Radical Trapping Technique

1998 ◽  
Vol 51 (12) ◽  
pp. 1113 ◽  
Author(s):  
Peter Dokolas ◽  
Steven M. Loer ◽  
David H. Solomon
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Abstraction ◽  
Hydrogen Atom Abstraction ◽  
Aromatic Solvent ◽  
Radical Trapping ◽  
Sterically Demanding ◽  
Butoxy Radical ◽  
Hydrocarbon Solution ◽  
Acyclic Hydrocarbons

The reaction of 3-methylpentane and 2,4-dimethylpentane toward t-butoxy radicals has been investigated, in neat and benzene solutions, by using the radical trapping technique. Abstraction occurs principally from the tertiary and secondary C-H reaction sites of 3-methylpentane and the tertiary position of 2,4-dimethylpentane. The tertiary and in particular secondary C-H reaction sites of 2,4-dimethylpentane are shown to be considerably less susceptible towards t-butoxy radical facilitated abstraction compared with the equivalent reaction sites of 3-methylpentane. As a result, the latter is three times as reactive as 2,4-dimethylpentane as a neat hydrocarbon solution and seven times as reactive in a diluted mixture of benzene. Diferences in selectivity and rate of hydrogen abstraction, between the substrates, are interpreted in terms of non-bonding interactions retarding t-butoxy radicals from approaching sterically demanding C-H reaction sites. The selectivity from 3-methylpentane is solvent-insensitive whereas abstraction from 2,4-dimethylpentane is modified in benzene. Further, the rate of hydrogen abstraction, from either substrate, to t-butoxy radical β-scission is considerably smaller in benzene. Both observations are interpreted in terms of t-butoxy radical solvation by the aromatic solvent.

Hydrogen atom abstraction from substituted toluenes by tert-butoxy radical

1968 ◽  
Vol 46 (16) ◽  
pp. 2752-2754 ◽  
Author(s):  
R. D. Gilliom ◽  
J. R. Howles
Keyword(s):  
Hydrogen Atom ◽  
Polar Effect ◽  
Hydrogen Atom Abstraction ◽  
Methyl Group ◽  
Tert Butyl ◽  
Hammett Correlation ◽  
Substituted Toluenes ◽  
Butoxy Radical

The relative rates of abstraction of benzylic hydrogen from substituted toluenes by tert-butoxy radicals generated from tert-butyl hypochlorite have been reexamined. Abstraction from para-methylanisole was shown to occur at the ether methyl as well as at the benzylic methyl group. For this reason the compound was excluded from an analysis of the polar effect. A slightly better Hammett correlation was obtained using sigma rather than sigma-plus values.

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