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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.
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83 citations
TL;DR: The reaction rate for cyclooctene epoxidation was increased 100- to 400-fold with axial coordination of imidazoles and phenolate and the reactivity of the oxoiron(IV) porphyrin pi-cation radical complex was drastically increased by theImidazole and Phenolate axial ligands.
Abstract: To study the effect of axial ligands on the electronic structure and reactivity of compound I of peroxidases and catalases, oxoiron(IV) porphyrin π-cation radical complexes with imidazole, 2-methylimidazole, 4(5)-methylimidazole, and 3-fluoro-4-nitrophenolate as the axial ligands were prepared by ozone oxidation of iron(III) complexes of 5,10,15,20-tetramesitylporphyrin (TMP) and 2,7,12,17-tetramethyl-3,8,13,18-tetramesitylporphyrin (TMTMP). These complexes were fully characterized by absorption, 1H, 2H, and 19F NMR, electron paramagnetic resonance (EPR), and electrospray ionization mass spectrometry (ESI-MS) spectroscopy. The characteristic absorption peak of compound I at approximately 650 nm was found to be a good marker for estimation of the electron donor effect from the axial ligand. The axial ligand effect did not change the porphyrin π-cation radical state, the a2u state of the TMP complexes, or the a1u radical state of both the TMTMP complexes and compound I. The ferryl iron and porphyrin π-catio...
82 citations
82 citations
01 Jan 2007
TL;DR: In this paper, the authors extended the analysis by considering a set of alkanes (RH = CH4, C2H6, C3H8, C4H10) and by including additional peroxy species (R ′ O 2 with R′ = H, CH, CH3, C 2H5, C 3H7, C 4H9, HC O, and CH3C O).
Abstract: A possible source of chain-branching in low temperature combustion is thermal decomposition of alkyl hydroperoxides (R′OOH). One way these species can be produced is via H atom abstraction reactions from alkanes (RH) by alkylperoxy radicals R ′ O 2 .An earlier study focussing on the abstraction from ethane by HO 2 , CH 3 O 2 and C 2 H 5 O 2 revealed that these reactions have a noticeable impact on calculated ignition times of ethane/O2 mixtures.Another outcome was that the abstraction rate constants for CH 3 O 2 and C 2 H 5 O 2 are virtually identical but smaller than that for HO 2 .The associated activation energies followed an Evans–Polanyi relationship while a common A-factor could be used to describe the kinetics of all three reactions within a factor of about 2–3.In this current study, we extend the investigation by (1) considering a set of alkanes(RH = CH4, C2H6, C3H8, C4H10) and (2) by including additional peroxy species ( R ′ O 2 with R′ = H, CH3, C2H5, C3H7, C4H9, HC O, and CH3C O). We present rate constants for a total of 32 reactions and analyze the data with respect to systematic trends in the reactivity. The results reveal that the rate constants decrease in the order acylperoxy > HO 2 > alkylperoxy. The reactivity of different C–H bonds follows the bond strengths. Overall the heat of reaction is found to be the dominant but not the only rate constant controlling parameter. The accuracy of the calculations and implications of the results are discussed.
82 citations
TL;DR: In this article, the authors have utilized ab initio quantum mechanics and transit quantum mechanics for the initial decomposition of HFCs under combustion conditions, using hydrogen atom abstraction by hydroxyl radicals.
Abstract: One of the fastest steps in the initial decomposition of HFCs under combustion conditions is hydrogen atom abstraction by hydroxyl radicals. We have utilized ab initio quantum mechanics and transit...
82 citations