The use of chemical probes to differentiate between polar and SET-hydrogen atom abstraction pathways involved in the reduction reaction promoted by an 8-Al-4 anion

1993 ◽  
Vol 58 (22) ◽  
pp. 5907-5914 ◽  
Author(s):  
Dennis D. Tanner ◽  
C. M. Yang
Keyword(s):  
Hydrogen Atom ◽  
Reduction Reaction ◽  
Hydrogen Atom Abstraction ◽  
Chemical Probes

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.

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.

Sign in / Sign up

Export Citation Format

Share Document