1981-80-2Relevant articles and documents
Mechanism of thermal decomposition of allyltrichlorosilane with formation of three labile intermediates: dichlorosilylene, allyl radical, and atomic chlorine
Boganov,Promyslov,Krylova,Zaitseva,Egorov
, p. 1216 - 1224 (2017/02/05)
It is experimentally found that allyltrichlorosilane dissociates under vacuum pyrolysis (~10–2 Torr) at temperatures above 1100 K to form three labile intermediates: allyl radical, dichlorosilylene, and monoatomic chlorine. On the basis of experimental and theoretical data obtained, it is shown that the decomposition reaction proceeds in two steps. The first step is a typical reaction of homolytic decomposition to two radicals (C3H5 and SiCl3) at the weakest Si—C bond. Due to weakness of the Si—Cl bond in the SiCl3 radical, the energy of which is even somewhat lower than the dissociation energy of the Si—C bond in starting AllSiCl3, this radical undergoes further dissociation to SiCl2 and Cl, thus resulting in three intermediates of different classes of highly reactive species formed from AllSiCl3.
Experimental study of the reaction between vinyl and methyl radicals in the gas phase. Temperature and pressure dependence of overall rate constants and product yields
Stoliarov, Stanislav I.,Knyazev, Vadim D.,Slagle, Irene R.
, p. 9687 - 9697 (2007/10/03)
The vinyl-methyl radicals are critical intermediates in hydrocarbon combustion systems with elementary reactions of CH3 and C2H3 influencing the rate and products of the overall combustion process. The vinyl-methyl cross-radical reaction was studied using laser photolysis/photoionization MS. C2H2 yields did not experience any pressure dependence at 310, 500, and 900 K. The C3H5 decreased with an increasing pressure, which was well resolved at 310 and 500 K. The overall C2H3 + CH3 rate constants and quantitative product yields were obtained in direct real-time experiments at 300-900 K and bath gas (He) density (3-12) x 1016 molecules/cc. The primary products of the C2H3 + CH3 reaction were propylene, acetylene, and allyl radicals. A mechanism consisting of two major routes was proposed, i.e., via direct abstraction of a hydrogen atom from the vinyl radical by the methyl radical resulting in the formation of acetylene and methane and via the formation of chemically activated propylene that can undergo collisional stabilization or further decomposition into allyl radical and hydrogen atom.
Polar effects on iodine atom abstraction by charged phenyl radicals
Heidbrink, Jenny L.,Thoen, Kami K.,Kenttaemaa, Hilkka I.
, p. 645 - 651 (2007/10/03)
The ability of differently substituted charged phenyl radicals (a class of distonic radical cations) to abstract an iodine atom from allyl iodide was systematically examined in the gas phase by using Fourier transform ion cyclotron resonance mass spectrometry. The reaction products and second-order reaction rate constants were determined for several radicals that differ by the type and/or number of substituents located in the ortho- and/or meta- position with respect to the radical site. All the radicals also carry a para-pyridinium group needed for mass spectrometric manipulation. These electron-deficient phenyl radicals react with allyl iodide by predominant iodine atom abstraction. The reaction is facilitated by the presence of neutral electron-withdrawing substituents, such as F, CF3, Cl, or CN. The extent of rate increase depends on the type and number of the substituents, as well as their location relative to the radical site. Based on molecular orbital calculations (PM3 and Becke3LYP/6-31G(d)+ZPVE), the indicated variations in the transition state energy are not related to enthalpic factors. Instead, the results are rationalized by polar effects arising from a variable contribution of a stabilizing charge transfer resonance structure to the transition state. A semiquantitative measure for the barrier-lowering effect of each substituent is provided by its influence on the electron affinity of the radical (the electron affinities were calculated by Becke3LYP/6-31+G(d) and AM1, which were found to produce similar values). Methyl substitution does not significantly affect the electron affinity, and accordingly, does not have a detectable effect on reactivity. Methyl groups located at ortho-positions are an exception, however. o-Methyl-substituted phenyl radicals undergo exothermic rearrangement to a benzyl radical in competition with iodine abstraction from allyl iodide.
