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Elementary reaction
About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.
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TL;DR: In this article, an elementary reaction mechanism was developed to model the experimentally observed loss of vinyl chloride by reaction with atomic hydrogen, as well as the observed products, based on quantum Rice-Ramsperger-Kassel (QRRK) analysis of the reactions of the energized adducts from the separately considered ipso and non-ipso additions.
Abstract: An elementary reaction mechanism has been developed to model the experimentally observed loss of vinyl chloride by reaction with atomic hydrogen, as well as the observed products. At the low-pressure, room temperature experimental conditions the consumption of C{sub 2}H{sub 3}Cl by reaction with H occurs primarily by nonipso attack by H on the =CH{sub 2} group to form (CH{sub 3}C{center_dot}HCl){sup {double_dagger}}. This energized complex then undergoes an H shift to form (C{center_dot}H{sub 2}CH{sub 2}Cl){sup {double_dagger}}, which decomposes to form Cl + CH{sub 2}=CH{sub 2}. Collisional stabilization of the original adduct is also important. Abstraction of Cl by H is negligible in these conditions. The authors` mechanism is based on quantum Rice-Ramsperger-Kassel (QRRK) analysis of the reactions of the energized adducts from the separately considered ipso and nonipso additions. The authors also utilized transition-state theory for the isomerization reaction, evaluated with literature rate constants and barriers. The authors extend the QRRK calculations to higher pressures and temperatures for use by the modeling community. A mechanistic pathway is presented to explain the formation of the various reaction products observed. 26 refs., 13 figs., 7 tabs.
20 citations
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TL;DR: In this article, the temperature dependence of electron transfer quenching of triplet excited neutral Pd−tetraphenylporphyrin was investigated in a series of isotropic solvents and in a nematic crystalline one.
Abstract: The temperature dependence of electron transfer quenching of triplet excited neutral Pd−tetraphenylporphyrin is investigated in a series of isotropic solvents and in a nematic crystalline one. Aromatic nitro compounds and quinones of different redox potentials are used as quenchers so that the quenching reaction is exergonic to slightly endergonic. The reactions of quenchers with the largest negative ΔG0 are diffusion controlled and thus have a positive enthalpy of activation, the quenchers with moderately negative ΔG0 values quench in the activation controlled realm with negative activation enthalpies, and the weakest quenchers again show positive activation enthalpies. An isokinetic relationship is found only in isotropic solvents, the first case of the isokinetic temperature being well above the temperatures of the experiments. Reactions with negative activation enthalpy are generally considered to have a pre-equilibrium, but it is shown that an elementary reaction may exhibit a negative enthalpy of ac...
20 citations
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TL;DR: In this paper, the effects of structure and size of nickel nanocatalysts on hydrogen production via water-gas shift reaction (WGSR) were investigated using a first-principles-based kinetic model.
20 citations
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TL;DR: In this paper, the authors investigated the energy partitioning quotient of an intramolecular substitution reaction and showed that the fraction of the reverse activation energy is released as kinetic energy.
Abstract: The loss of substituents X from molecular ions of ortho substituted 2-benzoyl pyridines has been investigated as a function of the dissociation energy of the C-X bond. Comparison of unimolecular and collisional induced decompositions of the resulting [M- XI' ions and reference ions arising from 3-hydroxypyrido[l,2alindole shows that cyclic fragment ions are formed in every case by an intramolecular substitution reaction with the exception of the parent compound (X=H), which gives rise to a mixture of [M-HI' ions with different structures. The heat of formation of the cyclic ion has been estimated experimentally and by calculation using thennochemical data, and from this value and the appearance energies, the activation energies of the reverse reactions have been evaluated for the different reaction systems. Measurement of the kinetic energy release during the substitution readions shows that only part of the reverse activation energy is released as kinetic energy. The energy partitioning quotient varies from 0.37 to 0.08 depending on the dissociation energy of the C-X bond or the reaction enthalpy. A sudden change in the energy partitioning quotient is observed with increasing exothermicity of the reaction, paralleling the behaviour of similar reaction systems. These results are interpreted as a demonstration of the influence of the variation of transition state position on the energy partitioning quotient. It has been shown recently2 that the partitioning of the excess potential energy of the transition states (or the activation energy of the reverse reactions F:) between the kinetic energy T, released during the reaction, and the internal energy F* of the products during the loss of ortho substituents from the molecular ions of substituted benz.alacetones depends strongly and systematically on the thermochemistry of the reaction or the position3 of the transition state on the reaction coordinate. Thus it appears that an investigation of the variation of the kinetic energy release and the energy partitioning quotient q = T/&f with structural changes of the reactant ions gives some insight into fundamental properties of elementary reactions of organic ions, which will be useful in testing mechanistic models of organic chemistry and linking them more closely to physical theories of chemical reactions. The loss of substituents from molecular ions of benzalacetones with formation of 2-rnethylbenzpyrylium ions4 can be regarded as an intramolecular aromatic substitution reaction,5 a well known reaction in organic chemistry. As a further example of this type of reaction the results of a detailed investigation of the loss of ortho substituents from the molecular ions of substituted 2-benzoyl pyridines la-lg (Scheme 1) are reported. The decomposition of the molecular ions of la-lg occurs by the three competing fragmentation pathways A-C shown in Scheme 1. Compound la exhibits large peaks due to [M-HI' and [M-CO]" ions in its 70eV mass spectrum, which are absent or of much lower relative abundance in the 70 eV mass spectra of
20 citations
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TL;DR: In this article, a theoretical analysis of carbon-deposition kinetics was developed to take into account a back-reaction in a simple kinetic case and has been applied to experimental data for deposition from C3O2 in the presence of CO.
20 citations