Dual-level direct dynamics studies for the reactions of dimethyl ether with hydrogen atom and methyl radical

2003 ◽  
Vol 24 (5) ◽  
pp. 593-600 ◽  
Author(s):  
Jia-Yan Wu ◽  
Jing-Yao Liu ◽  
Ze-Sheng Li ◽  
Xu-Ri Huang ◽  
Chia-Chung Sun
Keyword(s):  
Hydrogen Atom ◽  
Dimethyl Ether ◽  
Methyl Radical ◽  
Direct Dynamics

Mercury-photosensitized decomposition of dimethyl ether. Part I. Mechanism

1967 ◽  
Vol 45 (22) ◽  
pp. 2763-2766 ◽  
Author(s):  
L. F Loucks ◽  
K. J Laidler
Keyword(s):  
Mass Balance ◽  
Dimethyl Ether ◽  
Pressure Range ◽  
Reaction Vessel ◽  
No Decomposition ◽  
Methyl Radical ◽  
Reaction Conditions ◽  
Products Of Reaction

The mercury-photosensitized decomposition of dimethyl ether was investigated from 200 to 300 °C and over the pressure range 3 to 600 mm Hg. Measurements were made of the initial rates of formation of the products of reaction, which are CO, H2, C2H6, CH4, CH3OC2H5, and CH3OCH2CH2OCH3. It is concluded that the primary step involves a C—H split; there is no evidence for a primary C—O split. Over the range 200 to 300 °C the methoxymethyl radical, CH3OCH2, decomposed to give formaldehyde and a methyl radical, whereas at 30 °C no decomposition of the CH3OCH2 radical was detected. The mass balance is consistent with the mechanism proposed. The homogeneity of the reaction conditions was examined by varying the concentration of mercury in the reaction vessel.

Homolytic Substitution at Phosphorus: An Ab initio Study of the Reaction of Hydrogen Atom and Methyl Radical With Phosphine and Methylphosphine

1995 ◽  
Vol 48 (2) ◽  
pp. 175 ◽  
Author(s):  
CH Schiesser ◽  
LM Wild
Keyword(s):  
Hydrogen Atom ◽  
Ab Initio ◽  
Phosphorus Atom ◽  
Methyl Radical ◽  
Orbital Theory ◽  
Energy Barriers ◽  
Radical Intermediates ◽  
Phosphoranyl Radical ◽  
High Level ◽  
Homolytic Substitution

Homolytic substitution reactions of hydrogen atom and methyl radical at the phosphorus atom in phosphine and methylphosphine have been examined by high-level ab initio molecular orbital theory. MP4SDTQ/6-31G**//MP2(FC)/6-31G** calculations predict that free-radical attack at the phosphorus atom in phosphines is facile, with energy barriers of 14-33 kJ mol-1 and likely to involve hypervalent phosphoranyl radical intermediates. These intermediates, in turn, are found to have dissociative energy barriers of 10-31 kJ mol-1, depending on leaving group, and are unlikely to undergo pseudorotation prior to dissociation. MP5/6-31G**//MP2/6-31G** calculations indicate that permutational isomerism of phosphoranyl radical is likely to involve barriers of 145 and 127 kJ mol-1 for mechanisms involving transition states of D4h and C4v symmetry respectively.

The reaction of hydrogen atoms with ethylene

1970 ◽  
Vol 316 (1527) ◽  
pp. 575-591 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Rate Constant ◽  
Recombination Reaction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Hydrogen Atoms ◽  
Ethyl Radical ◽  
Cracking Reaction ◽  
Computer Calculations ◽  
First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

Transition state dynamics and a QM/MM model for the Cl– + C2H5Cl SN2 reaction

2004 ◽  
Vol 82 (6) ◽  
pp. 891-899 ◽  
Author(s):  
Lipeng Sun ◽  
Eunkyung Chang ◽  
Kihyung Song ◽  
William L Hase
Keyword(s):  
Hydrogen Atom ◽  
Transition State ◽  
Reaction Dynamics ◽  
Vibrational Frequencies ◽  
Dynamics Simulation ◽  
Rrkm Theory ◽  
Direct Dynamics ◽  
Sn2 Reaction ◽  
Classical Trajectories ◽  
Link Atom

A MP2/6-31G* direct dynamics simulation is used to study the dynamics of the central barrier [Cl-C2H5-Cl]– for the Cl– + C2H5 SN2 reaction. The majority of the trajectories move off the central barrier to form the Cl––C2H5Cl complex and appear to undergo efficient IVR as assumed by RRKM theory. However, some of the trajectories move directly to products without forming the complex, a non-RRKM result. A hydrogen atom link-atom QM/MM model is described for studying the dynamics of [X-CH2R-Y]– central barriers with the -R substituent. The model is used to calculate vibrational frequencies for the [Cl-C2H5-Cl]– central barrier.Key words: SN2 reaction dynamics, RRKM theory, QM/MM model, central barrier dynamics, direct dynamics classical trajectories.

Individual rate constants of methyl radical reactions in the pyrolysis of dimethyl ether

1977 ◽  
Vol 55 (23) ◽  
pp. 4128-4134 ◽  
Author(s):  
Andrew M. Held ◽  
Kim C. Manthorne ◽  
Philip D. Pacey ◽  
Howard P. Reinholdt
Keyword(s):  
Dimethyl Ether ◽  
Rate Constants ◽  
Flow System ◽  
Average Concentration ◽  
Radical Reactions ◽  
Methyl Radical ◽  
Warm Up ◽  
Secondary Reactions ◽  
Ultraviolet Absorption Spectroscopy ◽  
Individual Rate

Dimethyl ether was pyrolyzed in a flow system at 10 to 80 Torr and 1005 K. The average concentration of CH3 radicals in the reactor was measured by ultraviolet absorption spectroscopy. Product yields were measured by gas chromatography. The system was simulated using a computer program, taking into account the warm-up of the entering gas and the occurrence of secondary reactions. Rate constants were varied to find values consistent with experimental observations. The limiting, high pressure rate constant for the recombination of CH3 was estimated to be 1010.5 ± 0.5ℓ mol−1 s−1. Estimated rate constants for the reactions[Formula: see text]were 107.12 ± 0.2ℓ mol−1 s−1 and 107.5 ± 0.4ℓ mol−1 s−1, respectively.

A theoretical study of hydrogen—atom abstraction by methyl radical

Tetrahedron ◽  
1988 ◽  
Vol 44 (24) ◽  
pp. 7621-7625 ◽  
Author(s):  
J.M Lluch ◽  
J Bertran ◽  
J.J Dannenberg
Keyword(s):  
Hydrogen Atom ◽  
Theoretical Study ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radical

Initiation mechanisms in radical polymerizations : Reaction of cumyloxy radicals with methyl methacrylate and styrene

1982 ◽  
Vol 35 (10) ◽  
pp. 2013 ◽  
Author(s):  
E Rizzardo ◽  
AK Serelis ◽  
DH Solomon
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Methyl Methacrylate ◽  
Rate Constants ◽  
Polymer Structure ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Constant Rate ◽  
Radical Generation

Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60�) of dicumyl hyponitrite in methyl methacrylate and styrene. The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxyl. Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate. Styrene underwent only double-bond addition by both cumyloxy and methyl radicals. Some possible implications of these results for polymer structure are discussed. A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave k=7.7 × 1014exp(-13600/T) s-1 for the rate constant. Rate constants for the addition of cumyloxyl to methyl methacrylate (k ≈ 2 × 104 dm3 mol-1 s-1) and styrene (k≈2 × 105 dm3 mol-1 s-1) at 60�have been estimated.

Mercury-photosensitized decomposition of dimethyl ether. Part II. The thermal decomposition of the methoxymethyl radical

1967 ◽  
Vol 45 (22) ◽  
pp. 2767-2773 ◽  
Author(s):  
Leon F. Loucks ◽  
Keith J. Laidler
Keyword(s):  
Carbon Dioxide ◽  
Dimethyl Ether ◽  
Pressure Range ◽  
High Pressures ◽  
Rate Coefficient ◽  
Rate Coefficients ◽  
Methyl Radical ◽  
Lower Efficiency ◽  
First Order ◽  
Order Rate

The decomposition of the methoxymethyl radical, generated in the mercury-photosensitized decomposition of dimethyl ether, has been investigated over the temperature range 200 to 300 °C and the pressure range 3 to 600 mm Hg. The radical decomposes to give a formaldehyde molecule and a methyl radical. The effects of pressure and temperature on the first-order rate coefficient for the decomposition of the methoxymethyl radical have been examined in detail. The rate coefficient shows a pressure dependence over the full pressure range studied. The order of the decomposition is about 1.4 at the middle of the pressure range studied, with a lower order at higher pressures and a higher order at lower pressures. At 100 mm Hg the observed activation energy for the decomposition of the methoxymethyl radical is 24.8 kcal/mole.The first-order and second-order rate coefficients, k∞ and k0, corresponding to the limiting conditions of high pressures and low pressures respectively, have been evaluated as [Formula: see text]Kassel integrations have been carried out for the methoxymethyl radical and have been fitted to the experimental data. It is concluded that 8 or 9 normal modes contribute to the energization of the radical. The rate coefficient is increased by the presence of carbon dioxide, but carbon dioxide has a lower efficiency than dimethyl ether for the transfer of energy in the energization process.

Structure and Reactivity of Methyl Radical — Cyanide Ion Pairs in Crystal I and Crystal II of Acetonitrile

1974 ◽  
Vol 52 (15) ◽  
pp. 2840-2844 ◽  
Author(s):  
Estel Dean Sprague ◽  
Keiji Takeda ◽  
Jih Tzong Wang ◽  
Ffrancon Williams
Keyword(s):  
Hydrogen Atom ◽  
Hyperfine Splitting ◽  
Radical Anion ◽  
Strong Dependence ◽  
Ion Pairs ◽  
Hydrogen Atom Abstraction ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Cyanide Ion ◽  
Radical Reactivity

The extent of interaction between methyl radicals and cyanide ions produced in pairs by dissociative electron capture in the two solid phases of acetonitrile has been studied by e.s.r. using CD313CN. Although no interaction is observed when the radical–anion pairs are generated by photobleaching the acetonitrile dimer radical anion in Crystal I, a very weak interaction as evidenced by an isotropic 13C hyperfine splitting of 3.4 G is found for the corresponding species produced from the acetonitrile monomer radical anion in Crystal II. The rate of hydrogen atom abstraction by the methyl radical in Crystal I is at least a factor of 10 greater than in Crystal II at the same temperature over the range 77–113 K. These results show that the weak perturbation of the methyl radical by the cyanide ion does not enhance methyl radical reactivity in hydrogen atom abstraction. Evidence from 13C hyperfine splitting measurements on [Formula: see text] indicates that the configuration of the methyl radical is planar in these radical–anion pairs. It is emphasized that quantum mechanical tunneling provides a satisfactory explanation for the low apparent activation energies, the curved Arrhenius plots, and the abnormally large deuterium isotope effects which characterize hydrogen atom abstraction reactions by methyl radicals in glassy and crystalline solids at low temperatures. Moreover, since the tunneling rate is extremely sensitive to the width of the barrier, methyl radical reactivity is expected to show a very strong dependence on the precise geometry of the reacting partners in the solid state.

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