Directive effects in benzylic hydrogen atom abstraction. Part III. Chlorination of nuclear-substituted toluenes, diphenylmethanes, and ethylbenzenes

1973 ◽  
pp. 689 ◽  
Author(s):  
Kheng H. Lee ◽  
T. O. Teo
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Atom Abstraction ◽  
Substituted Toluenes

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.

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.

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

2005 ◽  
Vol 70 (11) ◽  
pp. 1769-1786 ◽  
Author(s):  
Luc A. Vannier ◽  
Chunxiang Yao ◽  
František Tureček
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Atom ◽  
Gas Phase ◽  
Computational Study ◽  
Hydrogen Atom Abstraction ◽  
Oh Radical ◽  
Free Energies ◽  
Intramolecular Hydrogen ◽  
Solvation Free Energies ◽  
Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

scholarly journals A cross-dehydrogenative C(sp3)−H heteroarylation via photo-induced catalytic chlorine radical generation

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Chia-Yu Huang ◽  
Jianbin Li ◽  
Chao-Jun Li
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Evolution ◽  
Alkyl Radical ◽  
Cobalt Catalyst ◽  
Alkylation Reaction ◽  
Hydrogen Atom Abstraction ◽  
Dehydrogenative Coupling ◽  
Radical Generation ◽  
Limited Scope

AbstractHydrogen atom abstraction (HAT) from C(sp3)–H bonds of naturally abundant alkanes for alkyl radical generation represents a promising yet underexplored strategy in the alkylation reaction designs since involving stoichiometric oxidants, excessive alkane loading, and limited scope are common drawbacks. Here we report a photo-induced and chemical oxidant-free cross-dehydrogenative coupling (CDC) between alkanes and heteroarenes using catalytic chloride and cobalt catalyst. Couplings of strong C(sp3)–H bond-containing substrates and complex heteroarenes, have been achieved with satisfactory yields. This dual catalytic platform features the in situ engendered chlorine radical for alkyl radical generation and exploits the cobaloxime catalyst to enable the hydrogen evolution for catalytic turnover. The practical value of this protocol was demonstrated by the gram-scale synthesis of alkylated heteroarene with merely 3 equiv. alkane loading.

Absolute Rate Constants for Hydrocarbon Autoxidation. Part XX. Oxidation of Some Organic Sulfides

1971 ◽  
Vol 49 (12) ◽  
pp. 2178-2182 ◽  
Author(s):  
J. A. Howard ◽  
S. Korcek
Keyword(s):  
Liquid Phase ◽  
Hydrogen Atom ◽  
Rate Constants ◽  
Hydrogen Atom Abstraction ◽  
Absolute Rate ◽  
Organic Sulfides

Absolute rate constants for the liquid phase autoxidation of some organic sulfides at 30 °C have been measured. The reactivities of organic sulfides towards t-butylperoxy radicals are equal to or somewhat less than the reactivities of structurally analogous ethers. The α-alkylthiylalkylperoxy radicals appear to be about 3–5 times more reactive in hydrogen atom abstraction than the α-alkoxyalkylperoxy radicals.

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