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.

Carbon addition and oxidation reactions in heterogeneous combustion and soot formation

Abstract: The contribution of radical sites as active sites in several carbon addition and oxidation reactions under combustion conditions is assessed by comparing predicted rates of reactions involving radical sites against experimental measurements. The types and strength of C−H bonds in the peripheries of PAH molecules and in the surfaces of carbonaceous solids are considered, and radical-site concentrations are computed assuming equilibration of hydrogen abstraction by H atom and hydrogen addition by H2. Computed populations of radical sites are consistent with observed trends in radical/parent concentration ratios measured in flames. Calculated extents of radical formation in PAH molecules and in the surfaces of carbonaceous solids in combustion are substantial, e.g., ≈0.1 to 0.3 radical sites per original C−H bond. For large PAH of interest as soot precursors, the estimated average number of radical sites per molecule is ≈5 to 7 with the distribution extending up to 10 or more. Rate coefficients based on the computed radical-site populations are comparable to experimentally determined rate coefficients in several cases including soot oxidation by O2 and soot growth by C2H2, assuming both of these reactions are additions involving radical sites in the soot, and soot and tar oxidation by OH, soot mass growth by tar addition, and reactive coagulation of soot precursors, assuming these reactions are radical recombinations. Calculated radical-site populations and measured concentrations of radicals in flames indicate that recombination of CH3, C3H3 and other small radicals with radical sites in tar and soot would contribute significantly to tar and soot formation if the recombination collision efficiencies are 0.1 to 1.

Hydrogen abstraction/acetylene addition revealed.

Abstract: For almost half a century, polycyclic aromatic hydrocarbons (PAHs) have been proposed to play a key role in the astrochemical evolution of the interstellar medium (ISM) and in the chemistry of combustion systems. However, even the most fundamental reaction mechanism assumed to lead to the simplest PAH naphthalene--the hydrogen abstraction-acetylene addition (HACA) mechanism--has eluded experimental observation. Here, by probing the phenylacetylene (C8 H6 ) intermediate together with naphthalene (C10 H8 ) under combustion-like conditions by photo-ionization mass spectrometry, the very first direct experimental evidence for the validity of the HACA mechanism which so far had only been speculated theoretically is reported.

Chemistry of the 2,5-didehydropyridine biradical : computational, kinetic,and trapping studies toward drug design

Abstract: A combined computation, kinetic, and trapping study of the 2,5-didehydropyridine biradical finds the hydrogen abstraction reaction to be tunable by protonation The observation of small amounts of pyridine products in the thermolysis of a C,N-dialkynylimine, or azaenediyne, only when the reaction occurs in the presence of moderate amounts of protic acid, is consistent with qualitative theoretical predictions as well as ab initio calculations at the CASSCF and CASMP2 levels The implication of these findings for a more selective antitumor agent is discussed