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.

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.

The reduction of aryl trifluoromethyl ketones by sodium borohydride. The hydride transfer process

1980 ◽  
Vol 58 (23) ◽  
pp. 2491-2496 ◽  
Author(s):  
Ross Stewart ◽  
K. C. Teo
Keyword(s):  
Hydrogen Atom ◽  
Sodium Borohydride ◽  
Substituent Effects ◽  
Reduction Reaction ◽  
Hydrogen Atom Abstraction ◽  
Close Correspondence ◽  
Amino Groups ◽  
Oxidation Processes ◽  
Trifluoromethyl Ketones ◽  
Selectivity Principle

The rates of reduction of 17 aryl trifluoromethyl ketones by sodium borohydride in 2-propanol have been measured. The rho (ρ) value is +3.12, excluding the 4-amino and 4-dimethylamino groups, which both lower the rate to a greater extent than their σ values predict. The close correspondence between substituent effects for hydride addition in the methyl and trifluoromethyl series (excluding the amino groups) suggests that normal substituent effects are to be expected for oxidation processes involving hydride removal in trifluoromethyl compounds. The present results are consistent with the oxidation of aryl trifluoromethyl carbinols by permanganate taking place by hydrogen atom abstraction. The effect of substituents on the rate of reduction of the trifluoromethyl ketones is almost identical to that on the equilibrium constant for formation of the ketone hydrates. The application of the reactivity–selectivity principle to the reduction reaction is also considered. Reduction of the 4-ethyl compound has ΔH≠ = 2.7 kcal mol−1 and ΔS≠ = −38 cal deg−1 mol−1

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.

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