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.

Valence Bond Calculations of Hydrogen Transfer Reactions: A General Predictive Pattern Derived from Theory

Abstract: Hydrogen abstraction reactions of the type X• + H−H‘ → X−H + H‘• (X = F, Cl, Br, I) are studied by ab initio valence bond methods and the VB state correlation diagram (VBSCD) model. The reaction barriers and VB parameters of the VBSCD are computed by using the breathing orbital valence bond and valence bond configuration interaction methods. The combination of the VBSCD model and semiempirical VB theory leads to analytical expressions for the barriers and other VB quantities that match the ab initio VB calculations fairly well. The barriers are influenced by the endo- or exothermicity of the reaction, but the fundamental factor of the barrier is the average singlet−triplet gap of the bonds that are broken or formed in the reactions. Some further approximations lead to a simple formula that expresses the barrier for nonidentity and identity hydrogen abstraction reactions as a function of the bond strengths of reactants and products. The semiempirical expressions are shown to be useful not only for the mode...

The production of vibrationally excited hydroxyl radicals under isothermal conditions by flash photolysis

Abstract: The flash photolysis of ozone in the presence of ammonia, hydrogen, hydrogen chloride, methane and water has been investigated under isothermal conditions. In each case the presence of vibrationally excited hydroxyl radicals has been shown spectroscopically. The concentration of these species is highest at the shortest time (i.e. during the photolysis flash) and decreases rapidly to below detectable limits within about 20 $\mu s$. The hydroxyl radical is produced by the reaction $O(^1D)+HR \rightarrow OH*+R+29 to 46 kcal$ rotationally cold but with up to at least two quanta of vibrational energy, the energy for which is supplied by the electronic energy of the oxygen atom. Under some conditions, the spectrum of oxygen molecules with up to 16 quanta of vibrational energy is also seen and shows that the reaction $O(^1D)+O\_3 \rightarrow O\_2*+O_2$ competes successfully with the hydrogen abstraction reaction.

Hydrogen abstraction and decomposition of bromopicrin and other trihalogenated disinfection byproducts by GC/MS.

Abstract: Tribromonitromethane (bromopicrin), dibromochloronitromethane, bromodichloronitromethane, and trichloronitromethane (chloropicrin) have been identified as drinking water disinfection byproducts (DBPs). They are thermally unstable and decompose under commonly used injection port temperatures (200−250 °C) during gas chromatography (GC) or GC/mass spectrometry (GC/MS) analysis. The major decomposition products are haloforms (such as bromoform), which result from the abstraction of a hydrogen atom from the solvent by thermally generated trihalomethyl radicals. A number of other products formed by radical reactions with the solvent and other radicals were also detected. The trihalonitromethanes also decompose in the hot GC/MS transfer line, and the mass spectra obtained are mixed spectra of the undecomposed parent compound and decomposition products. This can complicate the identification of these compounds by GC/MS. Trihalomethyl compounds that do not have a nitro group, such as tribromoacetonitrile, carbon t...

Combustion modeling and kinetic rate calculations for a stoichiometric cyclohexane flame. 1. Major reaction pathways.

Abstract: The Utah Surrogate Mechanism was extended in order to model a stoichiometric premixed cyclohexane flame (P = 30 Torr). Generic rates were assigned to reaction classes of hydrogen abstraction, β scission, and isomerization, and the resulting mechanism was found to be adequate in describing the combustion chemistry of cyclohexane. Satisfactory results were obtained in comparison with the experimental data of oxygen, major products and important intermediates, which include major soot precursors of C2−C5 unsaturated species. Measured concentrations of immediate products of fuel decomposition were also successfully reproduced. For example, the maximum concentrations of benzene and 1,3-butadiene, two major fuel decomposition products via competing pathways, were predicted within 10% of the measured values. Ring-opening reactions compete with those of cascading dehydrogenation for the decomposition of the conjugate cyclohexyl radical. The major ring-opening pathways produce 1-buten-4-yl radical, molecular ethyl...