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Methyl Radical (methyl + radical)
Selected AbstractsReaction of H + ketene to formyl methyl and acetyl radicals and reverse dissociationsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2003Jongwoo Lee Thermochemical properties for reactants, intermediates, products, and transition states important in the ketene (CH2CO) + H reaction system and unimolecular reactions of the stabilized formyl methyl (C·H2CHO) and the acetyl radicals (CH3C·O) were analyzed with density functional and ab initio calculations. Enthalpies of formation (,Hf°298) were determined using isodesmic reaction analysis at the CBS-QCI/APNO and the CBSQ levels. Entropies (S°298) and heat capacities (Cp°(T)) were determined using geometric parameters and vibrational frequencies obtained at the HF/6-311G(d,p) level of theory. Internal rotor contributions were included in the S and Cp(T) values. A hydrogen atom can add to the CH2 -group of the ketene to form the acetyl radical, CH3C·O (Ea = 2.49 in CBS-QCI/APNO, units: kcal/mol). The acetyl radical can undergo ,-scission back to reactants, CH2CO + H (Ea = 45.97), isomerize via hydrogen shift (Ea = 46.35) to form the slight higher energy, formyl methyl radical, C·H2CHO, or decompose to CH3 + CO (Ea = 17.33). The hydrogen atom also can add to the carbonyl group to form C·H2CHO (Ea = 6.72). This formyl methyl radical can undergo , scission back to reactants, CH2CO + H (Ea = 43.85), or isomerize via hydrogen shift (Ea = 40.00) to form the acetyl radical isomer, CH3C·O, which can decompose to CH3 + CO. Rate constants are estimated as function of pressure and temperature, using quantum Rice,Ramsperger,Kassel analysis for k(E) and the master equation for falloff. Important reaction products are CH3 + CO via decomposition at both high and low temperatures. A transition state for direct abstraction of hydrogen atom on CH2CO by H to form, ketenyl radical plus H2 is identified with a barrier of 12.27, at the CBS-QCI/APNO level. ,Hf°298 values are estimated for the following compounds at the CBS-QCI/APNO level: CH3C·O (,3.27), C·H2CHO (3.08), CH2CO (,11.89), HC·CO (41.98) (kcal/mol). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 20,44, 2003 [source] Radical annihilation of ,-ray-irradiated contact lens blanks made of a 2-hydroxyethyl methacrylate copolymer at elevated temperaturesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Young-Shang Lin Abstract The annihilation of the radicals in irradiated 2-hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main-chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2-diphenyl-1-picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25,45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second-order kinetics; these were different from the kinetics for the color formation and defect-controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Theoretical study on the gas-phase reaction mechanism between nickel monoxide and methane for syngas productionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 6 2009Hua-Qing Yang Abstract The comprehensive mechanism survey on the gas-phase reaction between nickel monoxide and methane for the formation of syngas, formaldehyde, methanol, water, and methyl radical has been investigated on the triplet and singlet state potential energy surfaces at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(2d, 2p) levels. The computation reveals that the singlet intermediate HNiOCH3 is crucial for the syngas formation, whereas two kinds of important reaction intermediates, CH3NiOH and HNiOCH3, locate on the deep well, while CH3NiOH is more energetically favorable than HNiOCH3 on both the triplet and singlet states. The main products shall be syngas once HNiOCH3 is created on the singlet state, whereas the main products shall be methyl radical if CH3NiOH is formed on both singlet and triplet states. For the formation of syngas, the minimal energy reaction pathway (MERP) is more energetically preferable to start on the lowest excited singlet state other than on the ground triplet state. Among the MERP for the formation of syngas, the rate-determining step (RDS) is the reaction step for the singlet intermediate HNiOCH3 formation involving an oxidative addition of NiO molecule into the CH bond of methane, with an energy barrier of 120.3 kJ mol,1. The syngas formation would be more effective under higher temperature and photolysis reaction condition. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] trans -Resveratrol Protects Embryonic Mesencephalic Cells from tert -Butyl HydroperoxideJOURNAL OF NEUROCHEMISTRY, Issue 1 2000Electron Param Abstract : In recent years, the antioxidant and other pharmacological properties of resveratrol, a natural product present in grapes and wine, have attracted considerable interest from the biomedical research community. In an examination of the potential neuroprotective properties of the compound, we have investigated the ability of resveratrol to protect rat embryonic mesencephalic tissue, rich in dopaminergic neurones, from the prooxidant tert -butyl hydroperoxide. Using the electron paramagnetic resonance (EPR) spin-trapping technique, the main radicals detected in cell suspensions were the tert -butoxyl radical and the methyl radical, indicating the one-electron reduction of the peroxide followed by a ,-scission reaction. The appearance of EPR signals from the trapped radicals preceded the onset of cytotoxicity, which was almost exclusively necrotic in nature. The inclusion of resveratrol in incubations resulted in the marked protection of cells from tert -butyl hydroperoxide. In parallel spin-trapping experiments, we were able to demonstrate the scavenging of radicals by resveratrol, which involved direct competition between resveratrol and the spin trap for reaction with the radicals. To our knowledge, this is the first example in which cytoprotection by resveratrol has been demonstrated by EPR spin-trapping competition kinetics to be due to its scavenging of the radicals responsible for the toxicity of a prooxidant. [source] Efficient synthesis of ethanol and acetic acid from methane and carbon dioxide with a continuous, stepwise reactorAICHE JOURNAL, Issue 5 2010W. Huang Abstract The synthesis of C2 -oxygenates such as ethanol and acetic acid accomplished by CH4 dissociation and subsequent CO2 insertion onto methyl radicals, named the stepwise reaction technology, has been demonstrated to be both feasible and efficient through initial experiments conducted in microreactor units. This article describes the development of this technology, highlighting the aforementioned stepwise technology using a dual-reactor system, which can ensure that two raw gases enter the reactor uninterruptedly and are not mixed after reaction. The system productivity for acetic acid and ethanol displayed efficiencies greater than 5,10 times that of previous microreactor units. The investigation of mechanism indicates that acetic acid arises from insertion of CO2 into MCHx, while ethanol is formed either by hydrogenation of acetic acid or by hydration of C2H4, which results from homo-coupling of CH4. The latter route is the preferred of the two. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Characterisation of sulphoxides by atmospheric pressure ionisation mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2005Patricia Wright An observation that a series of proprietary compounds containing a methyl thiophenyl group all underwent metabolic S-oxidation, and that the product ion spectra of the resulting S-oxides showed methyl radical loss under low-energy atmospheric pressure ionisation tandem mass spectrometry (API-MS/MS) conditions, has led to an investigation of the fragmentation of commercially available sulphoxides. The phenyl methyl sulphoxides studied do lose methyl radicals under MS/MS conditions on triple quadrupole mass spectrometers. In addition, the phenyl sulphoxides, with simple substituents other than a methyl group, also showed a tendency to lose the substituent as a radical. It was concluded that radical loss from these simple sulphoxides was characteristic of S-oxidation of these molecules. Radical losses, such as those reported here, are used in-house to distinguish S-oxidation from N- and C-oxidation in metabolism studies. Copyright © 2005 John Wiley & Sons, Ltd. [source] Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low TemperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Faezeh Bagheri-Tar Abstract Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane-to-oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions. On décrit le couplage oxydant du méthane (OCM) en présence d'une couronne CC dans un réacteur tubulaire étroit en verre à la pression atmosphérique et à des températures en dessous de 200°C. La couronne est créée en appliquant 2200 V entre une pointe et une électrode plate distantes de 1,5 mm. La sélectivité du C2 ainsi que la conversion du méthane sont des fonctions du rapport méthane-oxygène, du temps de séjour du gaz et du courant électrique. À un rapport de CH4/O2 de 5 et un temps de séjour d'environ 30 ms, un rendement de C2 de 23,1 % est obtenu. Les principaux produits de ce procédé sont l'éthane, l'éthylène, l'acétylène, ainsi que le CO et le CO2 avec des rapports de CO/CO2 aussi élevés que 25. On propose l'idée que le méthane est activé par des espèces d'oxygène électrophiles pour former des radicaux de méthyle et que les produits du C2 sont produits par un mécanisme consécutif, tandis que les COx se forment lors de réactions parallèles. [source] | ||||||||||