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.

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.

Photolysis of 4-Methyl 3-Hexanone and 2-Methoxy 3-Pentanone in Hydrocarbon Solution

1971 ◽  
Vol 49 (8) ◽  
pp. 1310-1314 ◽  
Author(s):  
L. P-Y. Lee ◽  
B. McAneney ◽  
J. E. Guillet
Keyword(s):  
Quantum Yield ◽  
Hydrogen Abstraction ◽  
Type I ◽  
Type Ii ◽  
Cage Effect ◽  
Predominant Type ◽  
Norrish Type ◽  
Hydrocarbon Solution ◽  
Membered Transition State ◽  
Made In

Studies of the photolysis of 4-methyl 3-hexanone and the iso-electronic 2-methoxy 3-pentanone have been made in hydrocarbon solution using light of wavelength 313 nm. The latter compound gives only Norrish type II products with a quantum yield of 0.19 ±.01. The former gives a predominance of type I products with a total quantum yield of 0.23 ±.01 and the quantum yield for type II is reduced to 0.10 ±.01. The predominant type I reaction appears to involve α-scission to give an ethyl and a 2-methyl butyryl radical, which suggests a "cage effect". It is suggested that the reason for the suppression of the type I reaction in 2-methoxy 3-pentanone is the greater ease of γ-hydrogen abstraction due to the presence of the oxygen atom in a six-membered transition state.

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