Photochemistry as a probe of the excited state properties of molecules. IV. A determination of the relative triplet reactivities of the carbon-nitrogen and carbon-oxygen chromophores of 4-acylpyrimidines. Photochemical cyclopropanol formation

ALEXANDER, ERDWARD C.; Jackson, Roy J.

doi:10.1021/ja00422a070

Cited by 11 publications

(2 citation statements)

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“…The higher stability of radicals possessing electron-withdrawing substituents can be explained by captodative stabilization of the ketyl radical site. Additionally, excited 2-acyl-substituted ketones can abstract a hydrogen atom either by oxygen or by nitrogen, and a 1-hydropyridinyl radical can rearrange to a ketyl radical. − The emissive CIDEP spectrum from the photolysis of 4-acetylpyridine in IPA proved that the hydrogen atom is abstracted by the carbonyl group in the T 1 (mainly n,π*) state . 1-Hydropyridyl radical was also observed, and it was likely produced by secondary reduction of ground-state 4-acetylpyridine by the 2-hydroxy-2-propyl radical.…”

Section: Resultsmentioning

confidence: 99%

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

2005

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[reaction: see text] Excited phenacyl and 3-pyridacyl esters of benzoic acid react with an excess of aliphatic alcohols in a chain reaction process involving hydrogen transfer from the ketyl radical intermediates, leading to benzoic acid in addition to acetophenone and 3-acetylpyridine, respectively, as the byproducts. While the maximum quantum yields reached 4 in both cases, the 2- or 4-pyridacyl ester photoreduction proceeded with the efficiency below 100% under the same conditions. The investigation indicates that a radical coupling between ketyl radicals, both formed from the excited ester by hydrogen abstraction from an alcohol, is accompanied by the elimination of benzoic acid from the ester ketyl radical itself. A partitioning between two reactions was found to be remarkably sensitive to the chromophore nature, such as a position of the nitrogen atom in the pyridacyl moiety. The magnitude of a radical chain process is dependent on the efficiency of consecutive steps that produce free radicals capable of a subsequent ester reduction. The driving force of a possible electron transfer from the ketyl radicals to the ester has been excluded on the basis of cyclic voltametry measurements. The observed quantum yields of photoreduction were found to be diminished by formation of relatively long-lived light absorbing transients, coproducts obtained apparently by secondary photochemical reactions. Additionally, it is shown that basic additives such as pyridine can further increase the efficiency of the photoreduction by a factor of 4. A radical nature of the reduction mechanism was supported by finding a large kinetic chain length of an analogous reaction initiated by free radicals generated thermally yet again when phenacyl or 3-pyridacyl benzoate was used. Both phenacyl and pyridacyl chromophores are pronounced to be valuable as the photoremovable protecting groups when high quantum and chemical yields of carboxylic acid elimination are important, but higher concentrations of the hydrogen atom donors are not destructive for a reaction system or are experimentally impractical.

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Section: Resultsmentioning

confidence: 99%

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

2005

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“…Since the DBE of benzene ring is 4, molecules with DBE less than 3 indicate double bond only (Korsten, 1997), and the absorption may be from the heteroatom functionality of CHNOS. For instance, 10.1029/2020GL087977 both chromopheres (like C¼N, C¼O, N¼N, N¼O, and C¼S) and auxochromes (like -NH,-OH,-SH) containing heteroatom can also contribute to molecular light absorption (Alexander & Jackson, 1976;Yu et al, 2005;Shindy, 2017). The portion of CHNOS with high DBE but low absorption may be due to carbonyl (Powelson et al, 2013), which contributes to unsaturation, but with substantially less absorption at 365 nm (Fan et al, 2019).…”

Section: Effect Of Molecular Conjugation On Brc B Absmentioning

confidence: 99%

Molecular Absorption and Evolution Mechanisms of PM_2.5Brown Carbon Revealed by Electrospray Ionization Fourier Transform–Ion Cyclotron Resonance Mass Spectrometry During a Severe Winter Pollution Episode in Xi'an, China

Zeng

Shen

Takahama

et al. 2020

Geophysical Research Letters

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Knowledge of the molecular-level chemistry of brown carbon (BrC) is important in reducing the uncertainties in aerosol radiative forcing. Time-resolved ambient PM 2.5 samples were collected during a severe pollution episode in January 2017 over Xi'an, China for a comprehensive nontarget and full scanning of BrC molecules and their absorption properties using electrospray ionization Fourier transform-ion cyclotron resonance mass spectrometry combined with partial least squares regression analysis, which apportioned the overall ultraviolet absorption to individual molecules. The estimated absorption of CHNO and CHNOS molecules exhibited nighttime prevalence, whereas CHOS, CHNS, CHN, CHO, CHS, and CH molecules presented a dynamic trend. Carbon conjugation was positively correlated with estimated absorption by CHO and CHNO molecules, while exhibiting a mixed relationship with CHNOS. Higher nitrogen content was associated with enhanced light-absorption properties of BrC molecules, while higher oxygen and sulfur content appeared to be associated with photobleaching during secondary transformation.Plain Language Summary Individual molecular absorption has significant implications for ambient brown carbon analysis, but existing studies mostly focused on bulk absorption properties for the sample as a whole. A novel method is presented here to evaluate individual brown carbon absorption at the molecular level through high resolution mass spectrometry, and partial least squares regression analysis was applied to PM 2.5 samples collected during a heavy pollution episode in Xi'an, China. Nitrogen-containing compounds were found to be the strongest contributor to brown carbon absorption, especially during the nighttime, while processes involving oxidation and sulfur addition appeared to weaken the molecular absorption. This study bridges the gap between real atmospheric PM 2.5 absorption and knowledge from controlled laboratory studies, which support these findings.

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ChemInform Abstract: PHOTOCHEMISTRY AS A PROBE OF THE EXCITED STATE PROPERTIES OF MOLECULES. IV. A A DETERMINATION OF THE RELATIVE TRIPLET REACTIVITIES OF THE CARBON‐NITROGEN AND CARBON‐OXYGEN CHROMOPHORES OF 4‐ACYLPYRIMIDINES. PHOTOCHEMICAL CYCLOPROPANOL FORMATION

ALEXANDER¹,

Jackson²

1976

Chemischer Informationsdienst

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Photochemistry as a probe of the excited state properties of molecules. IV. A determination of the relative triplet reactivities of the carbon-nitrogen and carbon-oxygen chromophores of 4-acylpyrimidines. Photochemical cyclopropanol formation

Abstract: Die Photolyse des Pyrimidins (I) in Benzol ergibt das Acetylderivat (II), für dessen Bildung eine Typ‐II‐Elirninierung verantwortlich ist, die durch die Triplett‐Carbonylgruppe eingeleitet wird.

Cited by 11 publications

References 2 publications

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

Molecular Absorption and Evolution Mechanisms of PM_2.5Brown Carbon Revealed by Electrospray Ionization Fourier Transform–Ion Cyclotron Resonance Mass Spectrometry During a Severe Winter Pollution Episode in Xi'an, China

ChemInform Abstract: PHOTOCHEMISTRY AS A PROBE OF THE EXCITED STATE PROPERTIES OF MOLECULES. IV. A A DETERMINATION OF THE RELATIVE TRIPLET REACTIVITIES OF THE CARBON‐NITROGEN AND CARBON‐OXYGEN CHROMOPHORES OF 4‐ACYLPYRIMIDINES. PHOTOCHEMICAL CYCLOPROPANOL FORMATION

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Photochemistry as a probe of the excited state properties of molecules. IV. A determination of the relative triplet reactivities of the carbon-nitrogen and carbon-oxygen chromophores of 4-acylpyrimidines. Photochemical cyclopropanol formation

Abstract: Die Photolyse des Pyrimidins (I) in Benzol ergibt das Acetylderivat (II), für dessen Bildung eine Typ‐II‐Elirninierung verantwortlich ist, die durch die Triplett‐Carbonylgruppe eingeleitet wird.

Cited by 11 publications

References 2 publications

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

Chain Mechanism in the Photocleavage of Phenacyl and Pyridacyl Esters in the Presence of Hydrogen Donors

Molecular Absorption and Evolution Mechanisms of PM2.5Brown Carbon Revealed by Electrospray Ionization Fourier Transform–Ion Cyclotron Resonance Mass Spectrometry During a Severe Winter Pollution Episode in Xi'an, China

ChemInform Abstract: PHOTOCHEMISTRY AS A PROBE OF THE EXCITED STATE PROPERTIES OF MOLECULES. IV. A A DETERMINATION OF THE RELATIVE TRIPLET REACTIVITIES OF THE CARBON‐NITROGEN AND CARBON‐OXYGEN CHROMOPHORES OF 4‐ACYLPYRIMIDINES. PHOTOCHEMICAL CYCLOPROPANOL FORMATION

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Molecular Absorption and Evolution Mechanisms of PM_2.5Brown Carbon Revealed by Electrospray Ionization Fourier Transform–Ion Cyclotron Resonance Mass Spectrometry During a Severe Winter Pollution Episode in Xi'an, China