Organic photochemistry. Part 99. A novel .gamma.-hydrogen abstraction ("Norrish-Type II") reaction upon S2 excitation of thiocamphor in the gas phase

1993 ◽  
Vol 115 (14) ◽  
pp. 6446-6447 ◽  
Author(s):  
Yuelie Lu ◽  
Dean Carlson ◽  
Harry Morrison
Keyword(s):  
Gas Phase ◽  
Hydrogen Abstraction ◽  
Type Ii ◽  
Norrish Type ◽  
Organic Photochemistry

Organic photochemistry with 6.7-eV photons: rigid homoallylic alcohols. An inverse Norrish type II rearrangement

1980 ◽  
Vol 102 (22) ◽  
pp. 6872-6874 ◽  
Author(s):  
Joel Studebaker ◽  
R. Srinivasan ◽  
Jose A. Ors ◽  
Thomas Baum
Keyword(s):  
Type Ii ◽  
Homoallylic Alcohols ◽  
Norrish Type ◽  
Organic Photochemistry

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

scholarly journals Structural Causes of Singlet/triplet Preferences of Norrish Type II Reactions in Carbonyls

2020 ◽  
Author(s):  
Keiran Rowell ◽  
Scott Kable ◽  
Meredith J. T. Jordan
Keyword(s):  
Hydrogen Abstraction ◽  
Conical Intersection ◽  
Quantum Yields ◽  
Type Ii ◽  
Structure Activity ◽  
Abstraction Reaction ◽  
Norrish Type ◽  
Close Proximity ◽  
Unsaturated Carbonyls ◽  
Hydrogen Abstraction Reaction

Photolysis thresholds are calculated for the Norrish Type II (NTII) intramolecular γ-hydrogen abstraction reaction in 22 structurally informative carbonyl species. The B2GP-PLYP excited state <i>S</i><sub>1</sub> and <i>T</i><sub>1</sub> thresholds agree well with triplet quenching experiments. However, many linear-response methods deliver poor <i>S</i><sub>1</sub> energetics, which is explained by a <i>S</i><sub>1</sub>/<i>S</i><sub>0</sub> conical intersection in close proximity to the <i>S</i><sub>1 </sub>transition state. Multiconfigurational CASSCF calculations confirm a conical intersection features across all carbonyl classes. <div><br></div><div>Structure–activity relationships are determined that could be used in atmospheric carbonyl photochemsitry modelling. This is exemplified for butanal, whose NTII quantum yields are too low when used as a ‘surrogate’ for larger carbonyls, since butanal lacks the γ-substitution that stabilises the 1,4- biradical. Reaction on <i>T</i><sub>1</sub> dominates only in species where the <i>S</i><sub>1</sub> thresholds are high — typically ketones. The α, β-unsaturated carbonyls cannot cleave the α–β bond, causing them to photoisomerise. A concerted <i>S</i><sub>0</sub> NTII mechanism is calculated to be viable and may explain the recent detection of NTII photoproducts in the photolysis of pentan-2-one below the <i>T</i><sub>1</sub> threshold.</div>

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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