Norrish Type II Photoelimination of Ketones: Cleavage of 1,4‐Biradicals Formed by γ‐Hydrogen Abstraction

Wagner, Peter J.; Klán, Petr

doi:10.1002/chin.200421253

Cited by 14 publications

(20 citation statements)

References 170 publications

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“…Photoenolization reactions have been thoroughly reviewed by Sammes in the 1970s, 51 recently by Klán et al, 52 and, to a modest extent, in several other reviews and book chapters. 8d,27,32,50,53 …”

Section: Arylcarbonylmethyl Groupsmentioning

confidence: 99%

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

et al. 2012

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Section: Arylcarbonylmethyl Groupsmentioning

confidence: 99%

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

et al. 2012

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“…T 1 NTIb thresholds are close to the maximum available energy of 400 kJ/mol and have negligible contribution to actinic photolysis (Zhu et al, 2009), T 1 NTIa thresholds are generally lower (Rowell et al, 2019), and this reaction dominates the photolysis QY of small carbonyls (Kirkbride and Norrish, 1931;Zhu et al, 2009). In larger carbonyls (alkyl chains lengths ≥ 4), excited state NTII intramolecular γ-H abstraction is also accessible (Wagner and Zepp, 1972;Wagner and Klán, 2004;Zhu et al, 2009).…”

Section: Other Carbonylsmentioning

confidence: 82%

Photo-initiated ground state chemistry: How important is it in the atmosphere?

Rowell

Kable

Jordan

2021

Preprint

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Abstract. Carbonyls are among the most abundant volatile organic compounds in the atmosphere. They are central to atmospheric photochemistry as absorption of near-UV radiation by the C=O chromophore can lead to photolysis. If photolysis does not occur on electronic excited states, non-radiative relaxation to the ground state will form carbonyls with extremely high internal energy. These “hot” molecules can access a range of ground state reactions. Up to nine potential ground state reactions are investigated at the B2GP-PLYP-D3/def2-TZVP level of theory for a dataset of 20 representative carbonyls. Almost all are energetically accessible under tropospheric conditions. Comparison with experiment suggests the most significant ground state dissociation pathways will be concerted triple fragmentation in saturated aldehydes, Norrish type III dissociation to form another carbonyl, and H2-loss involving the formyl H atom in aldehydes. Tautomerisation, leading to more reactive unsaturated species, is also predicted to be energetically accessible and is likely to be important when there is no low-energy ground state dissociation pathway, for example in α,β-unsaturated carbonyls and some ketones. The concerted triple fragmentation and H2-loss pathways have immediate atmospheric implication to global H2 production and tautomerisaton has implication to the atmospheric production of organic acids.

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“…In addition, photolysis of 1 did not yield any products that can be attributed to intramolecular H atom abstraction of the γ ‐H atom adjacent to the ester group (H γ ) , which is expected to yield o ‐methylacetophenone and the corresponding cyclobutanol (Scheme ). Thus, intramolecular H atom abstraction from the ortho ‐methyl substituent must be more efficient than that from the ester alkyl chain in ester 1 .…”

Section: Resultsmentioning

confidence: 99%

Photoenolization of o‐Methylvalerophenone Ester Derivative

Das

Lao

Guđmundsdóttir

2016

Photochem & Photobiology

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Photolysis of ester 1 in argon-saturated methanol and acetonitrile does not produce any product, whereas irradiation of 1 in oxygen-saturated methanol yields peroxide 2. Laser flash photolysis studies demonstrate that 1 undergoes intramolecular H atom abstraction to form biradical 3 (λmax ~340 nm), which intersystem crosses to form photoenols Z-4 and E-4 (λmax ~380 nm). Photoenols 4 decay by regenerating ester 1. With the aid of density functional theory calculations, it was concluded the photoenol E-4 does not undergo spontaneous lactonization or electrocyclic ring closure because the transition state barriers for these reactions are too large to compete with reketonization of E-4 to form 1.

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Norrish Type II Photoelimination of Ketones: Cleavage of 1,4‐Biradicals Formed by γ‐Hydrogen Abstraction

Cited by 14 publications

References 170 publications

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Photo-initiated ground state chemistry: How important is it in the atmosphere?

Photoenolization of o‐Methylvalerophenone Ester Derivative

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