2143-68-2Relevant articles and documents
Competition between hydrogen and deuterium abstraction by methyl radicals in isotopomerically mixed methanol glasses
Doba, Takahisa,Ingold, K. U.,Lusztyk, Janusz,Siebrand, Willem,Wildman, Timothy A.
, p. 2962 - 2970 (1993)
Rate parameters are reported for hydrogen and deuterium abstraction of methyl radicals embedded in glassy mixtures of CH3OH and CD3OD.The mole fraction of CH3OH in these isotopomeric mixture is 0, 0.05, 0.075, 0.10, 0.15, or 1.The nonexponential time dependence of the radical concentration is analyzed in terms of distributions of first-order rate constants.For the isotopomerically pure matrices, lognormal distributions describe the decay satisfactorily.The large difference between characteristic H and D transfer rate constants indicates tunneling.In the mixtures, there is competition between H and D abstraction processes which depends on the local structure about a radical, so that the corresponding rate parameters contain information about this structure.On the basis of earlier work , the analysis begins with the assumption that the structure about a radical resembles one of the crystalline phases of methanol.The entire set of decay curves is described by a (disordered) β-phase structure in which the radical replaces a methanol molecule and is located near the position associated with a methyl group.However, this static picture is inadequate because the radical can diffuse through the glass on the time scale of the kinetic measurements.Diffusion allows the radical to encounter more CH3OH molecules than would be expected for the static structure on a statistical basis - the effective mole fraction of CH3OH in the mixtures is higher than the analytical concentration.For the xH = 0.05 mixture, we estimate that on the average the radical encounters approximately 26 methanol molecules before abstraction occurs.This corresponds to diffusion over roughly 1100pm through the lattice.
Kinetics and Mechanism of the Reaction of CH3 and CH3O with ClO and OClO at 298 K
Biggs, Peter,Canosa-Mas, Carlos E.,Fracheboud, Jean-Marc,Marston, George,Shallcross, Dudley E.,Wayne, Richard P.
, p. 3045 - 3054 (1995)
A discharge-flow system equipped with a laser-induced fluorescence cell to detect the methoxyl radical and a quadrupole mass spectrometer to detect both the chlorine monoxide and chlorine dioxide radicals has been used to measure the rate constants for the reactions CH3 + ClO -> products (1) CH3O + ClO -> products (2) CH3 + OClO -> products (3) CH3O + OClO -> products (4) at T 298 K and P = 1-3 Torr.The observed products of these reactions are CH3O for reaction (1), HOCl for reaction (2), and CH3O and ClO for reaction (3).For reaction (4), CH3OCl is a possible product.The rate constants derived for reactions (1)-(4) are: k1 = (1.3 +/- 0.4)E-10 cm3 molecule -1 s-1; k2 = (1.3 +/- 0.3)E-11 cm3 molecule-1 s-1; k3 = (1.6 +/- 0.3)E-11 cm3 molecule-1 s-1; k4 = (1.5 +/- 0.5)E-12 cm3 molecule-1 s-1.The likely mechanism for (1)-(4) are briefly discussed.
Kinetic studies of the reactions CH3+NO2→products, CH3O+NO2→products, and OH+CH3C(O)CH3→CH3C(O)OH+CH3, over a range of temperature and pressure
Wollenhaupt, Matthias,Crowley, John N.
, p. 6429 - 6438 (2000)
The title reactions were investigated using pulsed laser photolysis combined with pulsed laser induced fluorescence detection of CH3O to determine the rate coefficients for CH3+NO2→products (3) and CH3O+NO2→products (5) as a function of temperature and pressure, and to estimate the yield of CH3 (and thus the yield of CH3C(O)OH) from the reaction of OH with CH3C(O)CH3 (2) at two different temperatures. Reaction 3 has both bimolecular and termolecular components: a simplified falloff parametrization with Fcent = 0.6 gives k3b0 = (3.2±1.3)×10-28(T/297)-0.3 cm6 s-1 and k3b∞ = (4.3±0.4)×10-11(T/297)-1.2 cm3 s-1 with CH3NO2 the likely product. The rate constant for the bimolecular reaction pathway to form CH3O+NO (3a) was found to be 1.9×10-11 cm-3 s-1. The low- and high-pressure limiting rate coefficients for reaction between CH3O and NO2 to form CH3ONO2 (5b) were derived as k5b0 = (5.3±0.3)×10-29(T/297)-4.4 cm6 s-1 and k5b∞ = (1.9±0.05)×10-11(T/297)-1.9 cm3 s-1, respectively. Although the final result is associated with some experimental uncertainty, we find that CH3 is formed in the reaction between OH and CH3C(O)CH3 at ≈50% yield at room temperature and 30% at 233 K.
Competing pathways for methoxy decomposition on oxygen-covered Mo(110)
Queeney,Friend
, p. 6067 - 6074 (1998)
The reactions of methanol (CH3OH) are investigated on a range of oxygen overlayers on Mo(110), with θO from ～0.5 to >1 ML, using a combination of vibrational spectroscopies and temperature-programmed reaction. Infrared spectroscopy identifies a common, tilted methoxy intermediate at high temperature on all overlayers studied; electron energy loss spectroscopy shows that this intermediate decomposes to deposit oxygen exclusively in high-coordination sites. While C-O bond scission to evolve gas-phase methyl radicals is the only reaction observed for methoxy on highly oxidized Mo(110), on the surface oxygen overlayers competition between dehydrogenation and methyl evolution is highly sensitive to oxygen coverage. The enhanced selectivity for hydrocarbon formation from methanol reaction on oxygen-modified Mo(110) relative to the clean surface is attributed to inhibition of dehydrogenation pathways rather than to marked changes in the C-O bond potential of methoxy.
High-temperature shock tube study of the reactions CH3 + OH → products and CH3OH + Ar → products
Vasudevan, Venkatesh,Cook, Robert D.,Hanson, Ronald K.,Bowman, Craig T.,Golden, David M.
, p. 488 - 495 (2008)
The reaction between methyl and hydroxyl radicals has been studied in reflected shock wave experiments using narrow-linewidth OH laser absorption. OH radicals were generated by the rapid thermal decomposition of tert-butyl hydroperoxide. Two different species were used as CH3 radical precursors, azomethane and methyl iodide. The overall rate coefficient of the CH3 + OH reaction was determined in the temperature range 1081-1426 K under conditions of chemical isolation. The experimental data are in good agreement with a recent theoretical study of the reaction. The decomposition of methanol to methyl and OH radicals was also investigated behind reflected shock waves. The current measurements are in good agreement with a recent experimental study and a master equation simulation.
Oxidation of alkyl ions, CnH2n+1+ (n = 1-5), in reactions with O2 and O3 in the gas phase
Williams, Skip,Knighton,Midey, Anthony J.,Viggiano,Irle, Stephan,Wang, Qingfang,Morokuma, Keiji
, p. 1980 - 1989 (2007/10/03)
Rate constants and product ion branching fractions are reported for the reactions of CH3+, C2H5+, s-C3H7+, s-C4H9+, t-C4H9+, and t-C5H11+ with O2 and O3 at 300 K in a variable-temperature selected-ion flow tube (VT-SIFT). The reaction rate constant for CH3+ with O3 is large and approximately equal to the thermal energy capture rate constant given by the Su-Chesnavich equation. The C2H5+, s-C3H7+, and s-C4H9+ ions are somewhat less reactive, reacting at approximately 7-46% of the thermal capture rate. The HCO+ and C2H3O+ ions are the major products in these reactions. The t-C4H9+ and t-C5H11+ ions are found to be unreactive, with rate constants -12 cm3 s-1, which is the present detection limit of our apparatus using this ozone source. Ozone is a singlet in its ground state, and ab initio calculations at the B3LYP/6-31G(d) level of theory indicate that reactant complexes can be formed, decreasing in stability with the size of alkyl chains attached to the cationic carbon atom. The decreasing reactivity of the alkyl ions with increasing order of the carbocation is attributed to a greatly reduced O3 binding energy. The ions listed above do not undergo two-body reactions with O2, k -13 cm3 s-1, despite the availability of reaction channels with exothermicities of several hudnred kilojoules per mole. Ab initio calculations at the B3LYP/6-31G(d) level of theory indicate that the O2 reaction systems form weak complexes with large C-O bond distances (repulsive at smaller distances) on the lowest energy triplet potential energy surface. Access to the singlet surface is required for bond formation; however, this surface is not accessible at thermal energies.
Kinetics of reductive N-O bond fragmentation: The role of a conical intersection
Lorance, Edward D.,Kramer, Wolfgang H.,Gould, Ian R.
, p. 15225 - 15238 (2007/10/03)
N-alkoxyheterocycles can act as powerful one-electron acceptors in photochemical electrontransfer reactions. One-electron reduction of these species results in formation of a radical that undergoes N-O bond fragmentation to form an alkoxy radical and a neutral heterocycle. The kinetics of this N-O bond fragmentation reaction have been determined for a series of radicals with varying substituents and extents of delocalization. Rate constants varying over 7 orders of magnitude are obtained. A reaction potential energy surface is described that involves avoidance of a conical intersection. A molecular basis for the variation of the reaction rate constant with radical structure is given in terms of the relationship between the energies of the important molecular orbitals and the reaction potential energy surface. Ab initio and density functional electronic structure calculations provide support for the proposed reaction energy surface.
