Hydrogen atom abstraction

About: Hydrogen atom abstraction is a research topic. Over the lifetime, 7059 publications have been published within this topic receiving 151781 citations.

Products and mechanisms of the gas phase reactions of NO3 with CH3SCH3, CD3SCD3, CH3SH and CH3SSCH3

Abstract: Products and mechanisms of the reaction between the nitrate radical (NO3) and three of the most abundant reduced organic sulphur compounds in the atmosphere (CH3SCH3, CH3SH and CH3SSCH3), have been studied in a 480 L reaction chamber using in situ FT-IR and ion chromatography as analytical techniques. In the three reactions, methanesulphonic acid was found to be the most abundant sulphur containing product. In addition the stable products SO2, H2SO4, CH2O, and CH3ONO2 were identified and quantified and thionitric acid-S-methyl ester (CH3SNO2) was observed in the i.r. spectrum from all of the three reactions. Deuterated dimethylsulphide (CD3SCD3) showed an isotope effect on the reaction Deuterated dimethylsulphide (CD3SCD3) showed an isotope effect on the reaction rate constant (kH/kD) of 3.8±0.6, indicating that hydrogen abstraction is the first step in the NO3+CH3SCH3 reaction, probably after the formation of an inital adduct. Based on the products and intermediates identified, reaction mechanisms are proposed for the three reactions.

Hydrogen Transfer Reactivity of a Ferric Bi-imidazoline Complex That Models the Activity of Lipoxygenase Enzymes.

Abstract: The mono-deprotonated ferric complex [Fe(Hbim)(H2bim)2](ClO4)2 (2) oxidizes organic substrates with weak C−H bonds. A hydrogen atom abstraction mechanism is indicated. The ΔH° for addition of H• to 2 (the strength of a N−H bond in 1) is determined to be 76 kcal/mol, consistent with the reactivity observed.

Studies on the photolytic breakdown of hydroperoxides and peroxidized fatty acids by using electron spin resonance spectroscopy. Spin trapping of alkoxyl and peroxyl radicals in organic solvents.

Abstract: Spin trapping using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) has been used to detect and distinguish between the carbon-centred, alkoxyl, and peroxyl radicals produced during the photolytic decomposition of hydroperoxides. Photolysis of tert-butyl and cumene hydroperoxides, and peroxidized fatty acids, in toluene, with low levels of u.v. light, is shown to lead to the initial production of alkoxyl radicals by homolysis of the oxygen-oxygen bond. Subsequent reaction of these radicals with excess hydroperoxide leads, by hydrogen abstraction, to the production of peroxyl radicals that can be detected as their corresponding adducts with the spin trap. Subsequent breakdown of these adducts produces alkoxyl radicals and a further species that is believed to be the oxidized spin-trap radical 5,5-dimethyl-1-pyrrolidone-2-oxyl. No evidence was obtained at low hydroperoxide concentrations, with either the cumene or lipid alkoxyl radicals, for the occurrence of beta-scission reactions; the production of low levels of carbon-centred radicals is believed to be due to the alternative reactions of hydrogen abstraction, ring closure, and/or 1,2 hydrogen shifts. Analogous experiments with 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO) led only to the trapping of alkoxyl radicals with no evidence for peroxyl radical adducts, this is presumably due to a decreased rate of radical addition because of increased steric hindrance.

Interactions of Dimethoxy Ethane with Li2O2 Clusters and Likely Decomposition Mechanisms for Li–O2 Batteries

Abstract: One of the major problems facing the successful development of Li–O2 batteries is the decomposition of nonaqueous electrolytes, where the decomposition can be chemical or electrochemical during discharge or charge. In this paper, the decomposition pathways of dimethoxy ethane (DME) by the chemical reaction with the major discharge product, Li2O2, are investigated using theoretical methods. The computations were carried out using small Li2O2 clusters as models for potential sites on Li2O2 surfaces. Both hydrogen and proton abstraction mechanisms were considered. The computations suggest that the most favorable decomposition of ether solvents occurs on certain sites on the lithium peroxide surfaces involving hydrogen abstraction followed by reaction with oxygen, which leads to oxidized species such as aldehydes and carboxylates as well as LiOH on the surface of the lithium peroxide. The most favorable site is a Li–O–Li site that may be present on small nanoparticles or as a defect site on a surface. The dec...

Theoretical and Laboratory Studies on the Interaction of Cosmic-Ray Particles with Interstellar Ices. I. Synthesis of Polycyclic Aromatic Hydrocarbons by a Cosmic-Ray-Induced Multicenter Mechanism

Abstract: Methane, ethylene, and acetylene ices were irradiated in a ultra-high vacuum vessel between 10 K and 50 K with 7.3 MeV protons as well as 9.0 MeV He2+ nuclei to simulate the interaction of galactic cosmic-ray particles with extraterrestrial, organic ices and to elucidate a mechanistic model to synthesize experimentally detected polycyclic aromatic hydrocarbons (PAHs). Theoretical calculations center on computer simulations of ion-induced collision cascades in irradiated methane targets. MeV ions induce hydrogen and carbon knock-on particles in elastic encounters with the target atoms. Each primary knock-on triggers one collision cascade with up to 70 suprathermal carbon atoms concentrated in one to two subcascades in 0.6-5 × 103 A3. At the end point of each single trajectory, every suprathermal carbon atom can form an individual reaction center of hydrogen abstraction and insertion in or addition to chemical bonds of a reactant molecule. In the relaxation phase of this energized volume, overlapping reaction zones likely form observed PAHs napthalene, phenanthrene/azulene, and coronene. This multicenter mechanism establishes a versatile route to synthesize complex molecules in extraterrestrial ices even at temperatures as low as 10 K within cosmic-ray-initiated single collision cascades.