Mechanistic Aspects of Gas-Phase Hydrogen-Atom Transfer from Methane to [CO].+and [SiO].+: Why Do They Differ?

Gas-phase pyrolysis of cyclopentanone and cyclohexanone azines results in the formation of iminyl radicals. These undergo ring cleavage to the ω-cyanoalkyl radicals, which stabilize, by internal hydrogen-atom transfer, to the corresponding α-cyanoalkyl radicals. Fragmentation of the latter yields acrylonitrile and alkyl radicals, which can recombine with the α-cyanoalkyl radicals to form α-alkylated nitriles. The mechanisms involved are discussed with reference to isotopic labellingstudies.

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Isomérisation des radicaux insaturés. III. Radicaux α,α,β-,α,β,γ- et α,α,γ-triméthallyles

Canadian Journal of Chemistry ◽

10.1139/v85-523 ◽

1985 ◽

Vol 63 (11) ◽

pp. 3168-3173 ◽

Cited By ~ 2

Author(s):

Hélène Deslauriers ◽

Guy J. Collin

Keyword(s):

Hydrogen Atom ◽

Gas Phase ◽

Internal Energy ◽

Transfer Process ◽

Hydrogen Atom Transfer ◽

Atom Transfer

α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0–nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively. Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes. An internal sigmatropic 1,4-hydrogen atom transfer process is part of the proposed mechanism to explain such products. Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C—C) bond, then one β(C—H), and, to a lesser extent, one central C—CH3 bond.

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Titelbild: Electron-Proton Decoupling in Excited-State Hydrogen Atom Transfer in the Gas Phase (Angew. Chem. 50/2015)

Angewandte Chemie ◽

10.1002/ange.201509372 ◽

2015 ◽

Vol 127 (50) ◽

pp. 15193-15193

Author(s):

Mitsuhiko Miyazaki ◽

Ryuhei Ohara ◽

Kota Daigoku ◽

Kenro Hashimoto ◽

Jonathan R. Woodward ◽

...

Keyword(s):

Excited State ◽

Hydrogen Atom ◽

Gas Phase ◽

Hydrogen Atom Transfer ◽

Atom Transfer ◽

Proton Decoupling

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Quantum Chemical Investigation on the Antioxidant Activity of Neutral and Anionic Forms of Juglone: Metal Chelation and Its Effect on Radical Scavenging Activity

Journal of Chemistry ◽

10.1155/2017/3281684 ◽

2017 ◽

Vol 2017 ◽

pp. 1-14 ◽

Cited By ~ 1

Author(s):

Aymard Didier Fouegue Tamafo ◽

Julius Numbonui Ghogomu ◽

Nyiang Kennet Nkungli ◽

Désiré Bikélé Mama ◽

Elie Younang

Keyword(s):

Hydrogen Atom ◽

Gas Phase ◽

Radical Scavenging Activity ◽

Radical Scavenging ◽

Hydrogen Atom Transfer ◽

Binding Energies ◽

Atom Transfer ◽

Scavenging Activity ◽

Metal Chelation ◽

Cu Ions

The chelation ability of divalent Mg, Ca, Fe, Co, Ni, Cu, Zn, and monovalent Cu ions by neutral and anionic forms of juglone has been investigated at DFT/B3LYP/6-31+G(d,p) level of theory in gas and aqueous phases. It is noteworthy that only the 1 : 1 stoichiometry was considered herein. The effects of these metals on the radical scavenging activity of neutral juglone were evaluated via the usual descriptors of hydrogen atom transfer. According to our results, metal chelation by the two forms of juglone was spontaneous and exothermic in both media. Based on the binding energies, Cu(II) ion showed the highest affinity for the ligands. QTAIM analyses identified the metal-ligand bonds as intermediate type interactions in all the chelates, except those of Ca and Mg. It was also found that the chelates were better radical scavengers than the ligands. In the gas phase, the scavenging activity of the compounds was found to be governed by direct hydrogen atom transfer, the Co(II) chelate being the most reactive. In the aqueous phase also, the sequential proton loss electron transfer was preferred by all the molecules, while the Cu(II) chelates were the most reactive.

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Tunneling rate constants for intramolecular hydrogen atom transfer reactions in solution

Journal de Chimie Physique ◽

10.1051/jcp/1996931783 ◽

1996 ◽

Vol 93 ◽

pp. 1783-1807 ◽

Cited By ~ 11

Author(s):

S Lee ◽

JT Hynes

Keyword(s):

Hydrogen Atom ◽

Rate Constants ◽

Hydrogen Atom Transfer ◽

Tunneling Rate ◽

Transfer Reactions ◽

Atom Transfer ◽

Atom Transfer Reactions ◽

Intramolecular Hydrogen

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Direct Cyclization of Alkenyl Thioester via Transition Metal‐hydrogen Atom Transfer/radical‐polar Crossover Mechanism

10.26434/chemrxiv.10247813.v1 ◽

2019 ◽

Author(s):

Shiori Date ◽

Kensei Hamasaki ◽

Karen Sunagawa ◽

Hiroki Koyama ◽

Chikayoshi Sebe ◽

...

Keyword(s):

Natural Products ◽

Hydrogen Atom ◽

Transition Metal ◽

Hydrogen Atom Transfer ◽

Synthetic Method ◽

Atom Transfer ◽

Reaction Conditions ◽

Hydride Hydrogen ◽

Sulfur Heterocycles ◽

One Step

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

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