scholarly journals Atmospheric deuterium fractionation: HCHO and HCDO yields in the CH<sub>2</sub>DO+O<sub>2</sub> reaction

2007 ◽  
Vol 7 (4) ◽  
pp. 10019-10041 ◽  
Author(s):  
E. Nilsson ◽  
M. S. Johnson ◽  
F. Taketani ◽  
Y. Matsumi ◽  
M. D. Hurley ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Ftir Spectroscopy ◽  
Molecular Oxygen ◽  
Molecular Hydrogen ◽  
Branching Ratio ◽  
Hydrogen Atom Transfer ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
Methoxy Radical ◽  
Deuterium Enrichment

Abstract. The formation of formaldehyde via hydrogen atom transfer from the methoxy radical to molecular oxygen is a key step in the atmospheric photochemical oxidation of methane, and in the propagation of deuterium from methane to molecular hydrogen. We report the results of the first investigation of the branching ratio for HCHO and HCDO formation in the CH2DO+O2 reaction. Labeled methoxy radicals (CH2DO) were generated in a photochemical reactor by photolysis of CH2DONO. HCHO and HCDO concentrations were measured using FTIR spectroscopy. Significant deuterium enrichment was seen in the formaldehyde product, from which we derive a branching ratio of 88.2±1.1% for HCDO and 11.8±1.1% for HCHO. The implications of this fractionation on the propagation of deuterium in the atmosphere are discussed.

scholarly journals Atmospheric deuterium fractionation: HCHO and HCDO yields in the CH<sub>2</sub>DO + O<sub>2</sub> reaction

2007 ◽  
Vol 7 (22) ◽  
pp. 5873-5881 ◽  
Author(s):  
E. J. K. Nilsson ◽  
M. S. Johnson ◽  
F. Taketani ◽  
Y. Matsumi ◽  
M. D. Hurley ◽  
...  
Keyword(s):  
Hydrogen Atom ◽  
Ftir Spectroscopy ◽  
Molecular Oxygen ◽  
Molecular Hydrogen ◽  
Branching Ratio ◽  
Hydrogen Atom Transfer ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
Methoxy Radical ◽  
Deuterium Enrichment

Abstract. The formation of formaldehyde via hydrogen atom transfer from the methoxy radical to molecular oxygen is a key step in the atmospheric photochemical oxidation of methane, and in the propagation of deuterium from methane to molecular hydrogen. We report the results of the first investigation of the branching ratio for HCHO and HCDO formation in the CH2DO + O2 reaction. Labeled methoxy radicals (CH2DO) were generated in a photochemical reactor by photolysis of CH2DONO. HCHO and HCDO concentrations were measured using FTIR spectroscopy. Significant deuterium enrichment was seen in the formaldehyde product, from which we derive a branching ratio of 88.2±1.1% for HCDO and 11.8±1.1% for HCHO. The implications of this fractionation on the propagation of deuterium in the atmosphere are discussed.

scholarly journals Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

2020 ◽  
Author(s):  
Han-Li Sun ◽  
Fan Yang ◽  
Wei-Ting Ye ◽  
Jun-Jie Wang ◽  
Rong Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Electrochemical Analysis ◽  
Hydrogen Atom Transfer ◽  
Redox Process ◽  
Photochemical Oxidation ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Wide Range ◽  
Selective Alkylation

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies and stoichiometric experiments. This unique redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides and various N-heterocycles) using a wide range of alkenes including moderately electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

A DFT mechanistic and kinetic study on the reaction of phloroglucinol with •OH in different media: Hydrogen atom transfer versus oxidation

2019 ◽  
Vol 18 (03) ◽  
pp. 1950017 ◽  
Author(s):  
Kgalaletso P. Otukile ◽  
Mwadham M. Kabanda
Keyword(s):  
Hydrogen Atom ◽  
Biological System ◽  
Reaction Pathway ◽  
Branching Ratio ◽  
Oxidation Mechanism ◽  
Phenoxyl Radical ◽  
Hydrogen Atom Transfer ◽  
Basis Set ◽  
Kinetic Properties ◽  
Atmospheric Conditions

A theoretical study on the reaction of phloroglucinol with •OH has been performed with the aim of elucidating the geometric, energetic and kinetic properties of the reaction as well as identifying the preferred reaction pathway. Three reaction mechanisms have been considered, namely, direct hydrogen atom abstraction, addition–elimination mechanism in the absence and in the presence of a base catalyst and oxidation mechanism in the absence and in the presence of O2. The study has been performed using the DFT/M06[Formula: see text]2X, DFT/BHHLYP and DFT/MPW1K methods in conjunction with either the 6-31++G(d,p) or the 6-311++G(3df,2p) basis set. The energetic parameters are influenced by the type of function utilized and the media in which the calculation is done. The direct hydrogen abstraction mechanism provides the smallest branching ratio with respect to the •OH addition mechanisms. The PG + •OH reaction under atmospheric conditions saturated with O2 would predominantly form tetrahydroxybenzene; the predominant product within the biological system would largely depend on physiological conditions; under pH [Formula: see text] 7 and with oxygen dissolved within the biological system, the preferred product would be tetrahydroxybenzene; however, if the reaction takes place in some part of the biological system where the pH [Formula: see text] 7, the preferred product would be the phenoxyl radical.

scholarly journals Dual Cobalt and Photoredox Catalysis Enabled Intermolecular Oxidative Hydrofunctionalization

2020 ◽  
Author(s):  
Han-Li Sun ◽  
Fan Yang ◽  
Wei-Ting Ye ◽  
Jun-Jie Wang ◽  
Rong Zhu
Keyword(s):  
Hydrogen Atom ◽  
Visible Light ◽  
Electrochemical Analysis ◽  
Hydrogen Atom Transfer ◽  
Redox Process ◽  
Photochemical Oxidation ◽  
Atom Transfer ◽  
Photoredox Catalysis ◽  
Wide Range ◽  
Selective Alkylation

A general protocol has been developed for the Markovnikov-selective intermolecular hydrofunctionalization based on visible-light-mediated Co/Ru dual catalysis. The key feature involves the photochemical oxidation of an organocobalt(III) intermediate derived from hydrogen atom transfer, which is supported by electrochemical analysis, quenching studies and stoichiometric experiments. This unique redox process enables the efficient branch-selective alkylation of pharmaceutically important nucleophiles (phenols, sulfonamides and various N-heterocycles) using a wide range of alkenes including moderately electron-deficient ones. Moreover, light-gated polar functionalization via organocobalt species was demonstrated.

scholarly journals A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

2009 ◽  
Vol 9 (2) ◽  
pp. 5679-5751 ◽  
Author(s):  
G. Pieterse ◽  
M. C. Krol ◽  
T. Röckmann
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Isotope ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Quantitative Information ◽  
Sensitivity Study ◽  
Reaction Scheme ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
The Individual

Abstract. The isotopic composition of molecular hydrogen (H2) produced by photochemical oxidation of methane (CH4) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H2). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH4 and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH4+Cl. The same approach is applied to VOCs, which are important precursors of H2 that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H2 product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H2 produced from CH4 and VOCs in a consistent way.

scholarly journals Diverting Radical-Anionic C-H Amidation to a C-N/C-O Cascade for the Construction of Hydroxyisoindolines from Unprotected Amides

2019 ◽  
Author(s):  
Quintin Elliott ◽  
Gabriel dos Passos Gomes ◽  
Christopher Evoniuk ◽  
Igor Alabugin
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Molecular Oxygen ◽  
Radical Anion ◽  
Reaction Path ◽  
Hydrogen Atom Transfer ◽  
Second Stage ◽  
Ch Activation ◽  
Computational Data ◽  
Extra Electron

<p>An intramolecular C(sp<sup>3</sup>)-H amidation proceeds in the presence of <i>t</i>-BuOK, molecular oxygen, and DMF. The success of this reaction hinges on the deprotonation of a mildly acidic N-H bond and selective radical activation of a benzylic C(sp<sup>3</sup>)-H bond towards hydrogen atom transfer (HAT)<i>. </i>DFT calculations suggest a thermodynamically favorable sequence of steps mediated by the generation of a radical-anion intermediate. As this intermediate starts to form a two-centered/three-electron (<i>2c,3e)</i>C-N bond, the extra electron is “ejected” into the π*-orbital of the aromatic core. The resulting cyclic radical-anion is readily oxidized by molecular oxygen to forge the C-N bond of the product. The transformation of a relatively weak reductant into a stronger reductant (i.e., “reductant upconversion”) allows one to use mild oxidants such as molecular oxygen. In contrast, the second stage of NH/CH activation forms a highly stabilized radical-anion intermediate incapable of electron transfer to molecular oxygen. Hence, the oxidation is impossible and an alternative reaction path opens via coupling between the radical anion intermediate and either superoxide or hydroperoxide radical. The hydroperoxide intermediate transforms into the final hydroxyisoindoline products under basic conditions. The use of TEMPO as an additive was found to activate less reactive amides. The combination of experimental and computational data outlines a conceptually new mechanism for the conversion of unprotected amides into hydroxyisoindolines proceeding as a sequence of C-H amidation and C-H oxidation.</p>

scholarly journals Diverting Radical-Anionic C-H Amidation to a C-N/C-O Cascade for the Construction of Hydroxyisoindolines from Unprotected Amides

2019 ◽  
Author(s):  
Quintin Elliott ◽  
Gabriel dos Passos Gomes ◽  
Christopher Evoniuk ◽  
Igor Alabugin
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Molecular Oxygen ◽  
Radical Anion ◽  
Reaction Path ◽  
Hydrogen Atom Transfer ◽  
Second Stage ◽  
Ch Activation ◽  
Computational Data ◽  
Extra Electron

<p>An intramolecular C(sp<sup>3</sup>)-H amidation proceeds in the presence of <i>t</i>-BuOK, molecular oxygen, and DMF. The success of this reaction hinges on the deprotonation of a mildly acidic N-H bond and selective radical activation of a benzylic C(sp<sup>3</sup>)-H bond towards hydrogen atom transfer (HAT)<i>. </i>DFT calculations suggest a thermodynamically favorable sequence of steps mediated by the generation of a radical-anion intermediate. As this intermediate starts to form a two-centered/three-electron (<i>2c,3e)</i>C-N bond, the extra electron is “ejected” into the π*-orbital of the aromatic core. The resulting cyclic radical-anion is readily oxidized by molecular oxygen to forge the C-N bond of the product. The transformation of a relatively weak reductant into a stronger reductant (i.e., “reductant upconversion”) allows one to use mild oxidants such as molecular oxygen. In contrast, the second stage of NH/CH activation forms a highly stabilized radical-anion intermediate incapable of electron transfer to molecular oxygen. Hence, the oxidation is impossible and an alternative reaction path opens via coupling between the radical anion intermediate and either superoxide or hydroperoxide radical. The hydroperoxide intermediate transforms into the final hydroxyisoindoline products under basic conditions. The use of TEMPO as an additive was found to activate less reactive amides. The combination of experimental and computational data outlines a conceptually new mechanism for the conversion of unprotected amides into hydroxyisoindolines proceeding as a sequence of C-H amidation and C-H oxidation.</p>

scholarly journals A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

2009 ◽  
Vol 9 (21) ◽  
pp. 8503-8529 ◽  
Author(s):  
G. Pieterse ◽  
M. C. Krol ◽  
T. Röckmann
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Isotope ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Quantitative Information ◽  
Sensitivity Study ◽  
Reaction Scheme ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
The Individual

Abstract. The isotopic composition of molecular hydrogen (H2) produced by photochemical oxidation of methane (CH4) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H2). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH4 and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH4+Cl. The same approach is applied to VOCs, which are important precursors of H2 that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H2 product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H2 produced from CH4 and VOCs in a consistent way.

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