6401-87-2Relevant articles and documents
Decomposition of Picolyl Radicals at High Temperature: A Mass Selective Threshold Photoelectron Spectroscopy Study
Reusch, Engelbert,Holzmeier, Fabian,Gerlach, Marius,Fischer, Ingo,Hemberger, Patrick
supporting information, p. 16652 - 16659 (2019/12/24)
The reaction products of the picolyl radicals at high temperature were characterized by mass-selective threshold photoelectron spectroscopy in the gas phase. Aminomethylpyridines were pyrolyzed to initially produce picolyl radicals (m/z=92). At higher temperatures further thermal reaction products are generated in the pyrolysis reactor. All compounds were identified by mass-selected threshold photoelectron spectroscopy and several hitherto unexplored reactive molecules were characterized. The mechanism for several dissociation pathways was outlined in computations. The spectrum of m/z=91, resulting from hydrogen loss of picolyl, shows four isomers, two ethynyl pyrroles with adiabatic ionization energies (IEad) of 7.99 eV (2-ethynyl-1H-pyrrole) and 8.12 eV (3-ethynyl-1H-pyrrole), and two cyclopentadiene carbonitriles with IE′s of 9.14 eV (cyclopenta-1,3-diene-1-carbonitrile) and 9.25 eV (cyclopenta-1,4-diene-1-carbonitrile). A second consecutive hydrogen loss forms the cyanocyclopentadienyl radical with IE′s of 9.07 eV (T0) and 9.21 eV (S1). This compound dissociates further to acetylene and the cyanopropynyl radical (IE=9.35 eV). Furthermore, the cyclopentadienyl radical, penta-1,3-diyne, cyclopentadiene and propargyl were identified in the spectra. Computations indicate that dissociation of picolyl proceeds initially via a resonance-stabilized seven-membered ring.
Homolytic dissociation of 1-substituted cyclohexa-2,5-diene-1-carboxylic acids: An EPR spectroscopic study of chain propagation
Jackson, Leon V.,Walton, John C.
, p. 1758 - 1764 (2007/10/03)
Hydrogen abstraction from 1-substituted cyclohexa-2,5-diene-1-carboxylic acids containing linear, branched and cyclic alkyl substituents, as well as allyl, propargyl (prop-2-ynyl), cyanomethyl and benzyl substituents, has been studied by EPR spectroscopy. For each carboxylic acid, EPR spectra of the corresponding cyclohexadienyl radicals were observed at lower temperatures, followed by spectra due to ejected carbon-centred radicals at higher temperatures. Rate constants, for release of the carbon-centred radicals from the cyclohexadienyl radicals, were determined from radical concentration measurements for the above range of substituents. The rate of cyclohexadienyl radical dissociation increased with branching in the 1-alkyl substituent and with electron delocalisation in the ejected carbon-centred radical; 3,5-and 2,6-dimethyl-substitution of the cyclohexadienyl ring led to reductions in the dissociation rate constants. Rate data for abstraction of bisallylic hydrogens from the cyclohexadienyl acids were also obtained for ethyl, n-propyl and isopropyl radicals. These results indicated a sharp drop in the rate of hydrogen abstraction as the degree of branching in the attacking radical increased. Small decreases in the hydrogen abstraction rate constants were observed for cyclohexadienes containing CO2R substituents.
Formation of the propargyl radical in the reaction of 1CH2 and C2H2: Experiment and modelling
Blitz, Mark A.,Beasley, Martin S.,Pilling, Michael J.,Robertson, Struan H.
, p. 805 - 812 (2007/10/03)
The propargyl radical, C3H3, is thought to be an important precursor to the formation of aromatic compounds and of soot in combustion systems. These radicals are produced during combustion by the reaction of 1CH2 with acetylene, which proceeds via a three well mechanism. A master equation model of this system is constructed with the aim of determining the branching ratio for formation of the propargyl radical as a function of temperature and pressure. The rate limiting step is the initial formation of cyclopropene from the reactants and a knowledge of the rate of this reaction is necessary for accurate modelling. The rate coefficient for the overall reaction was measured, as a function of temperature, using laser flash photolysis of a ketene-acetylene mixture. The reaction was monitored by laser induced fluorescence of 1CH2. Experimental results are presented and used in the master equation model, which shows that the yield, γ, of dissociation products H + C3H3 decreases with increasing pressure and that the onset of the decrease shifts to higher pressures as the temperature increases. At higher pressures and temperatures, there is an overlap in the timescales of dissociation of thermalised C3H4 and of the nascent C3H*4 formed from 1CH2 + C2H2, so that a simple description through time independent rate coefficients is no longer possible.
