Topic
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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01 Apr 1996TL;DR: In this article, a mass-spectrometric detection of HOBr with atomic chlorine, with oxygen and with hydroxyl radicals at 300 K using the discharge flow technique was performed.
Abstract: The reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass-spectrometric detection. The rate constants based on HOBr consumption have been determined to be k 1 = (8.0±0.4).10 -11 and k 2 = (3.1±0.2).10 -11 . For the reaction with OH radicals k 3 < 5.10 -13 was obtained. All rate constants are given in units cm 3 molecule -1 s -1 . The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCI and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH+BrCl → HOBr+Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr at T= 300 K was evaluated to be ΔH f 0 (HOBr) = - (60.22 ± 2) kJ.mol -1 .
21 citations
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TL;DR: The results show that the removal reactions of ethenol by H atom are selective: for abstractions, the hydrogen atom, linked to the oxygen atom, is the most reactive; while for additions, the preferred carbon site is the head "CH(2)═".
Abstract: Ethenol is a recently identified combustion intermediate. However, its chemistry remains unclear. In present work, the removal reactions of ethenol by H atom are investigated. The geometries of all species involved in the reaction are optimized at B3LYP/6-311++G(d,p), and their single point energies are extrapolated to the infinite-basis-set limit at the level CCSD(T). Energies are also calculated at G3B3, CBS-APNO, and CCSD(T)/6-311++G(3df, 2p) for comparison. A total of six elementary reactions, including four abstractions and two additions, with explicit transition states are investigated. The results show that the reactions are selective: for abstractions, the hydrogen atom, linked to the oxygen atom, is the most reactive; while for additions, the preferred carbon site is the head "CH(2)═". The rate constants are estimated in the temperature range 300-3000 K according to the conventional transition state theory with the Eckart tunneling model. The dominant channels are the two additions in the whole temperature range. The abstractions can be competitive at high temperature but still do not dominate. The calculated rate constants for the reverse reaction of (R6), syn-CH(2)═CHOH + H ↔ CH(3)·CHOH, are consistent with the available literature values. Finally, the Fukui functions are calculated to analyze the site reactivity.
21 citations
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TL;DR: Electrophilic aromatic sulfonation of benzene with sulfur trioxide is studied with ab initio molecular dynamics simulations in gas phase, and in explicit noncomplexing and complexing solvent models.
Abstract: Electrophilic aromatic sulfonation of benzene with sulfur trioxide is studied with ab initio molecular dynamics simulations in gas phase, and in explicit noncomplexing (CCl3F) and complexing (CH3NO2) solvent models. We investigate different possible reaction pathways, the number of SO3 molecules participating in the reaction, and the influence of the solvent. Our simulations confirm the existence of a low-energy concerted pathway with formation of a cyclic transition state with two SO3 molecules. Based on the simulation results, we propose a sequence of elementary reaction steps and a kinetic model compatible with experimental data. Furthermore, a new alternative reaction pathway is proposed in complexing solvent, involving two SO3 and one CH3NO2.
21 citations
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01 Aug 1991
TL;DR: In this article, the crucial role of O atoms in the formation of Cl2O4 formation was presented for either of the two mechanisms: (I) OClO + O + M ClO3 + O+M ClO4 + O3 + ClO2/N2 + M, or (II) ClO+ O + O4 + Cl 2O3+O2+N2+M, or(III) O+ClO+Cl 2O4+O3
Abstract: OClO/O2/N2 mixtures were photolyzed in a temperature controlled 4201 reaction chamber at temperatures between 249 and 300 K and total pressures between 0.5 and 1000 mbar. Initial OClO concentrations were in the range (1.7–5.7) · 1015 molecule/cm3. Reaction mixtures were analyzed in situ via long-path IR absorption using a Fourier-transform spectrometer. In some experiments product spectra were simultaneously monitored in the IR and the UV. Depending on reaction conditions, the product IR spectra were dominated by absorption bands of Cl2O3 or Cl2O4 or a mixture of both. Evidence is presented for the crucial role of O atoms in the Cl2O4 formation, suggesting either of the two mechanisms: (I) OClO + O + M ClO3 + M ClO3 + ClO + M Cl2O4 + M, or (II) OClO + ClO + M Cl2O3 + M, Cl2O3 + O + M Cl2O4 + M. Both the weak temperature dependence and the strong pressure dependence of the Cl2O4 yield support mechanism (I). In addition, Cl2O6 was detected as a minor product of OClO photolysis under certain reaction conditions, both by its IR and UV absorption.
21 citations
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TL;DR: In this article, the authors outline methods used to quantify reaction kinetics for catalytic cracking and describe how the rates of specific catalytic cycles are controlled by catalyst treatment (e.g., steaming) and process conditions (eg, conversion and temperature).
Abstract: Catalytic cracking of hydrocarbons takes place via elementary reactions such as initiation processes to form carbenium ions, olefin adsorption/desorption steps, isomerization, β-scission, oligomerization, and hydride ion transfer steps These elementary steps involving reactive carbenium ion surface intermediates are the essential components of catalytic cracking that lead to various catalytic cycles and their corresponding stoichiometric reactions This review outlines methods used to quantify reaction kinetics for catalytic cracking and describes how the rates of specific catalytic cycles are controlled by catalyst treatment (eg, steaming) and process conditions (eg, conversion and temperature)
21 citations