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.

Benz[a]anthracene photodegradation in the presence of known organic constituents of atmospheric aerosols

Abstract: Benz[a]anthracene photodegradation rates in toluene solutions containing co-solutes were compared using a photochemical turntable reactor. Each co-solute investigated was found at relatively high concentrations in atmospheric particulate matter. Benz-[a]anthracene photodegradation was accelerated by the presence of 9,10-anthraquinone, xanthone, 2-furaldehyde, 2,4-dimethylbenzaldehyde, 9,10-phenanthrenequinone, 2-acetylfuran, and furfuryl alcohol. Decay was inhibited by 7-benzanthrone. Other compounds had little or no effect on benz[a]-anthracene decay. Possible photochemical reaction mechanisms are discussed, and it is concluded that several competing mechanisms may be responsible, including electronic energytransferfollowed by reaction from the triplet state, singlet oxygen attack, and radical chain reactions initiated by hydrogen abstraction of aerosol constituents. The results suggest that particle organic composition can strongly influence polycyclic aromatic hydrocarbon photodegradation rates in atmospheric aerosols.

Detailed modeling of the molecular growth process in aromatic and aliphatic premixed flames

Abstract: A detailed kinetic model has been developed and used to simulate aromatic growth in premixed benzene and ethylene flames. The model considers the role of resonantly stabilized radicals in the growth of aromatic species, in addition to the hydrogen abstraction carbon addition (HACA) mechanism, which involves hydrogen abstraction to activate aromatics followed by subsequent acetylene addition. Model results show that the self-combination of resonantly stabilized radicalsin particular, the combination of cyclopentadienyl radicalsis the controlling pathway for the aromatic-ring growth. The kinetic model reproduces the experimental trends of these compounds already below the flame front and their decrease within the flame front, which has been observed experimentally but never predicted numerically. The reaction mechanism has been used to identify the different behaviors of aromatic growth in ethylene and benzene flames. Benzene formation is the rate-limiting step for aromatic growth in ethylene flames. C6H6 i...

Keto–Enol Tautomerization Triggers an Electrophilic Aldehyde Deformylation Reaction by a Nonheme Manganese(III)-Peroxo Complex

Abstract: Oxygen atom transfer by high-valent enzymatic intermediates remains an enigma in chemical catalysis. In particular, manganese is an important first-row metal involved in key biochemical processes, including the biosynthesis of molecular oxygen (through the photosystem II complex) and biodegradation of toxic superoxide to hydrogen peroxide by superoxide dismutase. Biomimetic models of these biological systems have been developed to gain understanding on the structure and properties of short-lived intermediates but also with the aim to create environmentally benign oxidants. In this work, we report a combined spectroscopy, kinetics and computational study on aldehyde deformylation by two side-on manganese(III)-peroxo complexes with bispidine ligands. Both manganese(III)-peroxo complexes are characterized by UV–vis and mass spectrometry techniques, and their reactivity patterns with aldehydes was investigated. We find a novel mechanism for the reaction that is initiated by a hydrogen atom abstraction reactio...

Ab initio QM/MM calculations show an intersystem crossing in the hydrogen abstraction step in dealkylation catalyzed by AlkB.

Abstract: AlkB is a bacterial enzyme that catalyzes the dealkylation of alkylated DNA bases. The rate-limiting step is known to be the abstraction of an H atom from the alkyl group on the damaged base by a FeIV-oxo species in the active site. We have used hybrid ab initio quantum mechanical/molecular mechanical methods to study this step in AlkB. Instead of forming an FeIII-oxyl radical from FeIV-oxo near the C–H activation transition state, the reactant is found to be an FeIII-oxyl with an intermediate-spin Fe (S = 3/2) ferromagnetically coupled to the oxyl radical, which we explore in detail using molecular orbital and quantum topological analyses. The minimum energy pathway remains on the quintet surface, but there is a transition between ISFeIII-oxyl and the state with a high-spin Fe (S = 5/2) antiferromagnetically coupled to the oxyl radical. These findings provide clarity for the evolution of the well-known π and σ channels on the quintet surface in the enzyme environment. Additionally, an energy decompositio...