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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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TL;DR: In this article, it is proposed that the dynamic electron polarization is due to the optically spin polarized triplets of the parent quinones and their subsequent hydrogen abstraction reaction with retention of polarization in the resultant semiquinone radicals.
Abstract: Electron spin resonance emission was observed from some photochemically produced semiquinone radicals in liquid isopropanol. It is proposed that the dynamic electron polarization is due to the optically spin polarized triplets of the parent quinones and their subsequent hydrogen abstraction reaction with retention of polarization in the resultant semiquinone radicals. Theoretical calculations have been carried out using typical zero field parameters for aromatic triplet molecules and the established assumption that the intersystem crossing rates to the three sublevels are unequal. Calculations reveal significant spin polarization of the triplets randomly oriented in an arbitrary magnetic field. Further treatment shows that when the triplet depolarization via relaxation is comparable to the chemical hydrogen abstraction rate, the resultant radical retains the polarization and is thus in the emissive mode.
140 citations
TL;DR: The reaction of H atoms with solid CO molecules was studied in this article, where the solid CO film deposited on the cold head of the cryocooler was reacted with H atoms by spraying the plasma-activated hydrogen gas over the surface of the sample.
140 citations
TL;DR: In this article, the photochemistry of several N-substituted 1,8-naphthalimides (NI) and 1,4,5,8naphthaldiimides(NDI) was studied using absorption and fluorescence spectroscopy and by laser flash photolysis (λexc = 355 nm).
Abstract: Despite the number and variety of their biological applications, the mechanisms of action of the photoactive naphthalenic imides have not yet been fully elucidated. In order to provide mechanistic insight, the photochemistry of several N-substituted 1,8-naphthalimides (NI) and 1,4,5,8-naphthaldiimides (NDI) has been studied using absorption and fluorescence spectroscopy and by laser flash photolysis (λexc = 355 nm). The lowest singlet state (S1) is mainly ππ* in nature for NI whereas nπ* character predominates for the NDI. This difference exerts a profound effect on subsequent reaction mechanisms: upon irradiation, only the NDI molecules can undergo intramolecular γ hydrogen abstraction. In the case of NP-III, a bishydroperoxy NDI derivative, this photoprocess (Φ = 0.03) leads to concomitant formation of an oxygen-centered radical (e = 21 600 M-1 cm-1 at 465 nm in acetonitrile) and release of the hydroxyl radical (•OH). All the compounds studied produce the triplet state (in acetonitrile, eT ≈ 10 500−11 ...
139 citations
TL;DR: Geometries, barriers, and enthalpies have been calculated at a variety of levels of theory for a test set of seven H-atom abstraction reactions: CH2X• + CH3Y → CH3X + CH2Y• as mentioned in this paper.
Abstract: Geometries, barriers, and enthalpies have been calculated at a variety of levels of theory for a test set of seven H-atom abstraction reactions: CH2X• + CH3Y → CH3X + CH2Y• for (X,Y) = (H,H), (F,H), (Li,H), (Li,F), (CN,H), (OH,H), and (OH,CN). The objective was to select reliable yet cost-effective theoretical procedures for studying H-atom abstraction reactions that involve carbon-centered radicals, to facilitate the study of these reactions in biological and polymerization applications. To this end, geometry optimizations have been observed to be relatively insensitive to the level of theory, although the Hartree-Fock (HF) and Moller-Plesset second-order perturbation (MP2) methods should be avoided for spin-contaminated systems. The QCISD/6-31G(d) method provided excellent agreement with CCSD(T)/6-311G(d,p) and would provide a suitable benchmark level of theory when the latter could not be afforded, whereas MPW1K/6-31+G(d,p) provided excellent low-cost performance and would thus be suitable for larger ...
139 citations
139 citations