Type II photoprocesses of phenyl ketones. Competitive .delta.-hydrogen abstraction and the geometry of intramolecular hydrogen atom transfers

1972 ◽  
Vol 94 (21) ◽  
pp. 7500-7506 ◽  
Author(s):  
Peter J. Wagner ◽  
Philip A. Kelso ◽  
Allen E. Kemppainen ◽  
Richard G. Zepp
Keyword(s):  
Hydrogen Atom ◽  
Hydrogen Abstraction ◽  
Type Ii ◽  
Hydrogen Atom Transfers ◽  
Intramolecular Hydrogen ◽  
Phenyl Ketones

scholarly journals Photochemistry of 2-Oxoacetates: from Mechanistic Insights to Profragrances and Bursting Capsules

2020 ◽  
Vol 74 (1) ◽  
pp. 39-48 ◽  
Author(s):  
Andreas Herrmann
Keyword(s):  
Carbonyl Compounds ◽  
Hydrogen Abstraction ◽  
Core Shell ◽  
Type Ii ◽  
Stimuli Responsive ◽  
Capsule Wall ◽  
Polymer Conjugates ◽  
Gas Formation ◽  
Norrish Type ◽  
Intramolecular Hydrogen

Photoirradiation of 2-oxoacetates (α-ketoesters) with UV-A light proceeds via an intramolecular hydrogen abstraction of the triplet state in a Norrish type II pathway to form carbonyl compounds, carbon monoxide and/or dioxide, and a series of other side products. This review gives a detailed overview of the mechanistic aspects of photooxidation by explaining the pathways that yield the major products formed in the presence or absence of oxygen. Furthermore, it demonstrates how the photoreaction can be used for the light-induced controlled release of fragrances from non-polymeric profragrances, polymer conjugates and core-shell microcapsules in applications of functional perfumery. In the case of microcapsules, the gas formation accompanying the Norrish type II fragmentation can generate an overpressure that expands or cleaves the capsule wall to release fragrances and thus provides access to multi-stimuli responsive delivery systems.

Mercury photosensitization of 1-hexene and cis-2-octene vapor. Intramolecular hydrogen abstraction of vibrationally excited π,π* triplet state

1976 ◽  
Vol 54 (20) ◽  
pp. 3117-3124 ◽  
Author(s):  
Yoshihisa Inoue ◽  
Setsuo Takamuku ◽  
Hiroshi Sakurai
Keyword(s):  
Transition State ◽  
Bond Cleavage ◽  
Hydrogen Abstraction ◽  
Minor Importance ◽  
Type Ii ◽  
Subsequent Reaction ◽  
Vibrationally Excited ◽  
Excited Triplet ◽  
Intramolecular Hydrogen ◽  
Membered Transition State

Upon mercury photosensitization, the vibrationally excited triplet of the simple alkenes 1-hexene and cis-2-octene undergoes an olefinic type II reaction consisting of an intramolecular 1,5-hydrogen abstraction via a six-membered transition state and subsequent reaction of the resulting biradical, in sharp contrast to the well established allylic C—C and C—H bond cleavage of alkenes without a γ-hydrogen. The cis–trans photoisomerization of cis-2-octene and other intramolecular hydrogen abstractions of minor importance occurring through unfavorable transition states were also observed. The mercury photosensitization of various cyclic and acyclic alkenes so far reported are comparatively discussed.

Synthesis of Spongidine A, D and Petrosaspongiolide L Methyl Ester Using Pyridine C-H Functionalization

2019 ◽  
Author(s):  
Florian Bartels ◽  
Manuela Weber ◽  
Mathias Christmann
Keyword(s):  
Natural Products ◽  
Methyl Ester ◽  
Hydrogen Atom ◽  
Phospholipase A2 ◽  
Late Stage ◽  
Hydrogen Atom Transfer ◽  
Ring System ◽  
Tetracyclic Core ◽  
Intramolecular Hydrogen ◽  
Phospholipase A2 Inhibitors

<div>An efficient strategy for the synthesis of the potent phospholipase A2 inhibitors spongidine A and D is presented. The tetracyclic core of the natural products was assembled via an intramolecular hydrogen atom transfer‐initiated Minisci reaction. A divergent late‐stage functionalization of the tetracyclic ring system was also used to achieve a concise synthesis of petrosaspongiolide L methyl ester.</div>

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.

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