- The 213.8-nm Photochemistry of Gaseous 1,3-Butadiene and the Structure of Some C3H3 Radicals
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A systematic study of the 213.8-nm (zinc line ) photochemistry of 1,3-butadiene has been made either in the absence or in the presence of various additives - such as radical scavengers (O2,NO,DI) and collisional quenchers - in the gas phase (pressure between 1 and 500 Torr).The major fate of the photoexcited 1,3-butadiene molecule is isomerization to the 1,2-butadiene structure which may then decompose to methyl and C3H3 radicals (Φ = 0.64 +/- 0.04 at 1 Torr of 1,3-butadiene).Minor processes include decomposition to the acetylene + ethylene couple (Φ = 0.22 +/- 0.02) or to vinylacetylene (Φ = 0.038 +/- 0.003) and molecular hydrogen.These two minor processes occur from different excited states.Some 2-butyne (Φ / = 10, the highest ratio used, Φ(allene + propyne)/ Φ(CH3D) = 0.72 and a fraction of the C3H3 radicals are still not accounted for (reaction with 1,3-butadiene and/or recombination ?).The relative energies obtained by ab initio RHF-SCF geometry optimizations for the doublet electronic state of the C3H3 radical structures are E(propargyl) 2B1 state) is the lowest energy one.There are probably at least two distinct C3H3 radical structures (different states) present in the far-UV photolysis of 1,3-butadiene.
- Collin, Guy J.,Deslauriers, Helene,Mare, George R. de,Poirier, Raymond A.
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Read Online
- An acelylenically of a diene compound and/or method of manufacturing
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Provided is a novel method for producing a compound having acetylene bonds and/or a diene. The method for producing a compound having acetylene bonds and/or a diene is characterized in that at least one selected from the group consisting of ketone compound (I), ketone compound (II), aldehyde compound (III), aldehyde compound (IV), and aldehyde compound (V) is dehydrated in the presence of a catalyst wherein a carrier containing silica supports at least one selected from the group consisting of compounds containing group 1 metal elements, compounds containing group 2 metal elements, group 1 metal elements, and group 2 metal elements.
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Paragraph 0427; 0428; 0437-0445
(2017/03/28)
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- Metal ions do not play a direct role in the formation of carbon-carbon triple bonds during reduction of trihaloalkyls by CrII or V II
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Carbyne radicals: Reactions of trihaloalkyl compounds with Cr2+ or V2+ in aqueous solutions yield alkynes and other products. Stepwise halogen abstractions from the trihaloalkyls form alkyl carbyne triradicals in solution. These radicals undergo coupling reactions, producing triply bonded alkyne molecules (see scheme). This process is not metal-assisted and does not occur in the coordination sphere of the metal ions.
- Levy, Ophir,Bino, Avi
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supporting information
p. 15944 - 15947
(2013/02/23)
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- Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4 (methylacetylene and allene), C3H6 (
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The reactions of the CH radical with several unsaturated hydrocarbons C2H2 (acetylene), C2H4 (ethylene), C3H4 (methyl-acetylene and allene), C3H 6 (propene) and C
- Loison, Jean-Christophe,Bergeat, Astrid
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body text
p. 655 - 664
(2009/05/07)
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- Nucleophilic reactivity of 1-zirconacyclopent-3-ynes: Carbon-carbon bond formation with aldehydes
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Nucleophilic reactions of 1,1-bis(η5-cyclopentadienyl)-1-zirconacyclopent-3-yne (1) with proton and aldehydes were studied. The reaction with HCl gave a mixture of 2-butyne and 1,2-butadiene. Complex 1 reacted with benzaldehyde to give 1-phenyl-2-methyl-2,3-butadien-1-ol (3) in moderate yields in the presence of a proton source such as triethylammonium hydrochloride, while it gave 2-methylene-1-phenyl-3-buten-1-ol (4) on using triethylammonium tetraphenylborate.
- Suzuki, Noriyuki,Watanabe, Takaaki,Hirose, Takuji,Chihara, Teiji
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p. 5317 - 5321
(2008/03/12)
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- Solvent extraction
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In a method for the solvent extraction of butadiene from a mixture of hydrocarbons having four carbon atoms per molecule, which method inherently produces tars, the extraction process is operated with a tar loading level, relative to the solvent employed, of no more than about 1.6 wt. %.
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Page/Page column 4-6
(2008/06/13)
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- Kinetics and products of propargyl (C3H3) radical self-reactions and propargyl-methyl cross-combination reactions
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Propargyl and methyl radicals were produced through the 193-nm excimer laser photolysis of mixtures of C3H3Cl/He and CH3N2CH3/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self-reactions and propargyl-methyl cross-combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C6H6 isomers. The rate constant determination in the propargyl-methyl mixed radical system yielded a value of (4.0±0.4)×10-11 cm3 molecule-1 s-1 for propargyl radical combination reactions and a rate constant of (1.5±0.3)×10-10 cm3 molecule-1 s-1 for propargyl-methyl cross-combination reactions. The products of the methyl-propargyl cross-combination reactions were two isomers of C4H6, 1-butyne (about 60%) and 1,2-butadiene (about 40%).
- Fahr, Askar,Nayak, Akshaya
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p. 118 - 124
(2007/10/03)
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- UV laser-induced photolysis of silacyclopent-3-ene: Unseparable photochemistry of reactant and product for chemical vapour deposition of Si/C/H polymer
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UV laser-induced photolysis of silacyclopent-3-ene in the gas phase is a clean extrusion of silylene yielding buta-1,3-diene. Silylene self-polymerisation and consequent deposition of SinH2n agglomerates is precluded by concurrently occurring photolysis of buta-1,3-diene. The solid polymeric deposit being produced through polymerisation steps involving both H2Si: and the products of the buta-1,3-diene photolysis makes the reaction suitable for chemical vapour deposition of Si/C/H films.
- Pola, Josef,Ouchi, Akihiko,Urbanova, Marketa,Koga, Yoshinori,Bastl, Zdenek,Subrt, Jan
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p. 246 - 250
(2007/10/03)
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- Use of but-1-yne as a probe for the characterization of the basicity of alkali-exchanged zeolites
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But-1-yne has been adsorbed at room temperature on a series of LiNa, Na and CsNaX and Y zeolites and also on CsNaX,9Cs and CsNaY,9Cs samples containing nine Cs atoms occluded by a unit cell. An IR study of the 3000-2800 cm-1 frequency range clearly showed that but-1-yne isomerized into but-2-yne on CsNaX,9Cs whereas the observation of a band near 1950 cm-1 in the case of CsNaY,9Cs characterized the formation of buta-1,2-diene. Such partial transformation of but-1-yne to isomers did not occur on LiNa and Na samples, allowing one to study the basicity of such zeolites from the v(≡CH) shift which decreases in the following order: NaX > LiNaX > NaY > LiNaY. The main feature is the observation of at least two perturbed v(≡CH) bands for the NaX and NaY samples, revealing the heterogeneity of the basic sites. This result is discussed taking into account the presence of cations in different positions.
- Lavalley, Jean-Claude,Lamotte, Jean,Travert, Arnaud,Czyzniewska, Jolanta,Ziolek, Maria
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p. 331 - 335
(2007/10/03)
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- Homolytic Bond Dissociation Enthalpies of the C-H Bonds Adjacent to Radical Centers
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Homolytic bond dissociation enthalpies (BDEs) at 0 and 298 K of the C-H bonds adjacent to various radical centers have been obtained from ab initio CBS-4 (complete basis set) model calculations and experimental data available in the literature. The BDEs of the G-H bonds adjacent to the radical centers derived from 11 saturated hydrocarbons were found to be 33.5 ±3 kcal/mol at 298 K. The BDEs of the C-H bonds adjacent to nine allylic and benzylic radical centers were found to be 48 ±3 kcal/mol at 298 K, but the benzylic C-H BDE of the PhCH2CH2 radical was found to be only 29.7 and 30.5 kcal/mol at 0 and 298 K, respectively. The BDEs of the vinylic C-H bonds adjacent to four vinylic radical centers were found to be 35.5 ±3.5 kcal/mol at 298 K. The BDEs of the vinylic C-H bonds adjacent to three allylic radical centers were found to be 56.5 ±3 kcal/ mol at 298 K. These results suggest that the radical centers weaken the adjacent C-H bond strengths by about 50-70 kcal/mol. The calculated BDEs agree within ±2 kcal/mol with most of the available experimental results. Isomerization enthalpies of butenes and pentenes have been obtained. Substituent effects on BDEs have also been examined.
- Zhang, Xian-Man
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p. 1872 - 1877
(2007/10/03)
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- Decomposition of 2-methylfuran. Experimental and modeling study
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The thermal reactions of 2-methylfuran were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1100-1400 K and with overall densities of approx. 3 × 10-5 mol/cm3. A large number of products resulting from unimolecular cleavage of the ring and consecutive free radical reactions were obtained under shock heating. The unimolecular decomposition is initiated by two parallel channels: (1) 1,2-hydrogen atom migration from C(5) to C(4) and (2) a methyl group migration from C(2) to C(3) in the ring. Each channel is followed by two parallel modes of ring cleavage. In the first channel, breaking the O - C(2) and the C(4) - C(5) bonds in the ring yields CO and different isomers of C4H6, whereas breaking of the O - C(2) and the C(3) - C(4) bonds yields CH2CO and two isomers C3H4. In the second channel, breaking the O - C(5), and C(2) - C(3) bonds in the ring yields again CO and isomers of C4H6, whereas in the second mode O - C(5), C(2) - C(3), and C(3) - C(4) are broken to yield CO, C2H2, and C2H4. The four C4H6 isomers in decreasing order of abundance were 1,3-butadiene, 1-butyne, 1,2-butadiene, and 2-butyne. The major decomposition product is carbon monoxide. The rate constant for its overall formation is estimated to be kCO = 1015.88 exp(-78.3 × 103/RT) s-1, where R is expressed in units of cal/(K mol). Other products that were found in the postshock samples in decreasing order of abundance were C4H4, C2H2, CH4, p-C3H4, C2H6, C2H4, a-C3H4, C6H6, C4H4O, C3H6, and C4H2. The total decomposition of 2-methylfuran in terms of a first order rate constant is given by ktotal = 1014.78 exp(-71.8 × 103/RT) s-1. This rate and the production rate of carbon monoxide are slightly higher than the ones found in the decomposition of furan. An oxygen-carbon mass balance among the decomposition products was obtained. A reaction scheme composed of 36 species and some 100 elementary reactions accounts for the product distribution over the temperature range covered in this study. First order Arrhenius rate parameters for the formation of the various reaction products are given, a reaction scheme is suggested, and results of computer simulation and sensitivity analysis are shown. Differences and similarities in the reactions of furan and 2-methylfuran are discussed.
- Lifshitz,Tamburu,Shashua
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p. 1018 - 1029
(2007/10/03)
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- Vibrational overtone activation of methylcyclopropene
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Laser vibrational overtone activation has been used to investigate the reaction channel competition in the isomerization of 1-methylcyclopropene (MCPene). The vibrational overtone activation of three types of CH stretches (methyl, methylenic, and olefinic) in the 5vCH and 6vCH transitions initiated the isomerization and all three products (2-butyne, 1,3-butadiene, and 1,2-butadiene) were detected by gas chromatography. Stern-Volmer plots were constructed for the appearance of each individual product and the derived experimental specific rate coefficients were compared to those of the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The rate coefficients for the 6vCH transitions were in good agreement with the predicted values but those for the 5vCH transition were as much as a factor of 5 too large. Product ratios of 1,3-butadiene to 2-butyne and 1,2-butadiene to 2-butyne were independent of pressure. In general, these ratios were lower than the RRKM predicted ratios due to collisional deactivation. No evidence of mode specific behavior was observed in these product yield ratios.
- Snavely,Grinevich,Hassoon,Snavely
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p. 5845 - 5851
(2007/10/03)
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- Thermal Decomposition of 1-Butyne in Shock Waves
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1-Butyne diluted with Ar was heated behind reflected shock waves over the temperature range of 1100 - 1600 K and the total density range of 1.36*10-5 - 1.75*10-5 mol/cm3.Reaction products were analyzed by gas-chromatography.The progress of the reaction was followed by IR laser kinetic absorption spectroscopy.The products were CH4, C2H2, C2H4, C2H6, allene, propyne, C4H2, vinylacetylene, 1,2-butadiene, 1,3-butadiene, and benzene.The present data were successfully modeled with a 80 reaction mechanism. 1-Butyne was found to isomerize to 1,2-butadiene.The initial decomposition was dominated by 1-butyne -> C3H3 + CH3 under these conditions.Rate constant expressions were derived for the decomposition to be k7 = 3.0*1015 exp(-75800 cal/RT) s-1 and for the isomerization to be k4 = 2.5*1013 exp(-65000 cal/RT) s-1.The activation energy 75.8 kcal/mol was cited from literature value and the activation energy 65 kcal/mol was assumed.These rate constant expressions are applicable under the present experimental conditions, 1100 - 1600 K and 1.23 - 2.30 atm.
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Oki, Takashi,Kawano, Hiroyuki
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p. 321 - 330
(2007/10/02)
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- Thermal Isomerization and Decomposition of 2-Butyne in Shock Waves
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The thermal isomerization and decomposition of 2-C4H6 behind reflected shock waves with 1100 5 3 were studied by UV kinetic absorption spectroscopy, IR laser kinetic absorption spectroscopy, and gas-chromatographic analysis of reaction products.The major products of the pyrolysis were 1,2-butadiene, 1,3-butadiene, CH4, C2H2, C2H6, allene, propyne, C4H2, vinylacetylene, and benzene. 1,3-butadiene and 1,2-butadiene were produced before the appearance of any other decomposition products.This fact means that the very fast isomerization of 2-butyne take place before the decomposition.The present data were successfully modeled with a 80 reaction mechanism which included the isomerizations among 1- and 2-butynes and 1,2- and 1,3-butadienes and the decomposition of these C4H6 isomers.From the modeling, the following rate constants of the isomerizations were obtained: 2-butyne = 1,3-butadiene (k = (3.0 x 1E13) exp(-65.0 kcal/RT) s-1). and 2-butyne = 1,2-butadiene (k = (3.0 x 1E13) exp(-67.0 kcal/RT) s-1), where the activation energies, 65 and 67 kcal/mol, were estimated from literature data.We discussed the possible route of the isomerizations of 2-butyne to 1,3- and 1,2-butadienes.
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Ninomiya, Natsuhiko,Oshita, Hidekazu,Kawano, Hiroyuki
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p. 10977 - 10983
(2007/10/02)
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- Mechanism of CH2.+ Transfer from Distonic Ions X-CH2.+ (X=CH2O, CH2CH2) to ?- and n-Electron Bases in the Gas Phase. A Fourier Transform Ion Cyclotron Resonance (FTICR) Study Supplemented by ab initio MO Calculations
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The reactions of acetonitrile, propyne, acetylene, trimethylsilylacetylene, and tetramethylsilane, with distonic ions CH2XCH2.+ are studied in the gas phase using Fourier Transform Ion Cyclotron Resonance (FTICR) mass spectrometry.In line with previous studies, CH2.+ is transferred to the electron lone-pair of the nitrogen atom of CH3CN to generate CH3CN-CH2.+ (4); upon collisional excitation, this ion undergoes competitive losses of H. and CH..While both neutrals originate from the "methylene" unit of 4, detailed studies employing labeledsubstrates and using various types of collision experiments reveal an intriguing dissociation pattern in that the dissociations are preceded by two intramolecular hydrogen migrations giving rise to CH3C(H)=NCH.+ (6) and CH3C=N(H)CH.+ (7).While 6 serves as intermediate en route to loss of H. from the "CH" moiety, 7 is the actual precursor to generate, by loss of CH., protonated acetonitrile, CH3CNH+ (12) (Scheme 5).In addition, 12 is formed by bimolecular proton transfer.In this reaction, translationally excited CX3CN-CY2.+* (X, Y = H, D) transfers X+ to neutral CX3CN to generate CX3CNX+ (Scheme 4).The bimolecular proton transfer as well as the intramolecular isomerizations of 4 to 6 and 7 are subject to very large kinetic isotope effects.In the transfer of CH2.+ to CH3CCH two products are formed .+ (16) and CH2=C=CHCH3.+ (17) presumably via intermediate 18 (Scheme 6)>; the latter is formed by addition of CH2.+ to the less hindered carbon atom of HCCCH3 reflecting the higher stability of the so-formed intermediate compared with addition to C-2.Reactions of 2 and 3 with HCCH do not result in the formation of a detectable CH2.+-transfer product.When using CH2CH2CH2.+ (2) the reaction is prohibited by the endothermicity to generate the initial complex (structurally related to 18).On the other hand, when CH2OCH2.+ (3) is employed, the intermediate of CH2.+ transfer is formed with sufficient energy to split off a hydrogen atom.Preliminary experiments with silicon-containing molecules, like Si(CH3)4 or HCCSi(CH3)3, demonstrate that the favored processes of these neutrals with 2 and 3 are due to charge transfer (in the form of an electron or an anion like CH3- or C2H-) from the silicon-containing molecule to the distonic ions.The experimental results obtained for CH3CN/CH2.+ system are supported by ab initio MO calculations (3-21G/3-21G + ZPVE).
- Rusli, Ridwan D.,Schwarz, Helmut
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p. 535 - 540
(2007/10/02)
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- Selective Lanthanide-catalysed Reactions. Catalytic Properties of Sm and Yb Metal Vapour Deposition Products
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The characteristics of lanthanide catalysts obtained when Sm and Yb were vaporized into a frozen organic (tetrahydrofuran, benzene and methylcyclohexane) matrix (77 K) were investigated.These low-valent, highly dispersed lanthanide particles (indicated as Sm/THF, Sm/benzene, Yb/THF, Yb/benzene etc.) were catalytically active and selective for hydrogenation and isomerization.Samarium usually showed a greater activity than ytterbium.Olefin hydrogenation obeyed the rate law v=kPH, suggesting that the reaction is controlled by catalytic activation of hydrogen.The molecular isotopic identity of hydrogen was conserved during the hydrogenation.Yb/THF and Yb/benzene were active for partial hydrogenation of benzene to cyclohexene.For the hydrogenation of olefins and acetylenes the substrate specificity was high; thus C-C double bonds were more readily reduced than triple bonds.The samarium and ytterbium catalysts discriminate between terminal and internal C-C triple bonds, only internal CC bonds (but-2-yne and pent-2-yne) being reduced very selectively in contrast to acetylene, methylacetylene and but-1-yne.Solid base character of the lanthanide provides a cause for these differences in catalytic properties.
- Imamura, Hayao,Kitajima, Keiji,Tsuchiya, Susumu
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p. 1647 - 1654
(2007/10/02)
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- Studies on the Thermal Conversion of Long-chain Alkynes at High Temperatures in the Gas Phase
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In the gas phase pyrolysis of long-chain alkynes C5 to C9 at 773 to 873 K, a remarkable portion of molecular reaction (retro-ene analogous decompositions as well as cycloisomerizations of the parent alkynes to cyclopentenes alkylated in 3-position) takes place besides the thermal conversion of the starting compounds via radical chain processes.The different products were separated by GC and the main products identified by means of different methods.The mechanisms of formation of the major products are discussed.
- Ondruschka, B.,Zimmermann, G.,Ziegler, U.,Kopinke, F.-D.,Teuber, M.
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p. 273 - 284
(2007/10/02)
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- Selective Hydrogenation of Internal and Terminal CC Bonds on Rare Earth Catalysts Formed by Metal Vapor Deposition
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The rare earth catalysts obtained when Sm and Yb were vaporized into a frozen organic matrix exhibited selective hidrogenation of various acetylenic derivatives.Sm/THF and Yb/THF discriminated between internal and terminal triple bonds.
- Imamura, Hayao,Kitajima, Keiji,Tsuchiya, Susumu
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p. 249 - 250
(2007/10/02)
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- The isomerization of 1-methylcyclopropene: A multichannel unimolecular reaction induced by overtone excitation
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The distribution of products resulting from the isomerization of gas phase 1-methylcyclopropene (1) induced by C-H stretch overtone excitation has been studied in a search for mode specific effects.Quantum yields for the disappearance of 1 have been determined as a function of the total pressure of a mixture of 1 and methylenecyclopropane and of the added bath gases SF6 and Ar using a combination of intracavity dye laser photolysis and end product analysis by gas chromatography.These data, together with the ratios of the yields of the major isomerization products, are adequately reproduced by RRKM theory and a weak collisional energy transfer model: no evidence for mode specifity is obtained.The experimental data demonstrate the importance of inefficient collisional energy transfer but allow some conclusions to be drawn concerning the applicability of RRKM theory which are not strongly dependent upon the details of the energy transfer model.
- Baggott, J. E.,Law, D. W.
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p. 900 - 906
(2007/10/02)
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- LA PHOTOCHIMIE DE L'ISOPRENE GAZEUX DANS LA REGION DE L'ULTRAVIOLET TRES LOINTAIN
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Yields of various products have been measured in the photolysis of isopropene at 184.9, 213.8, and 228.8 nm and at pressures between 1 and 400 Torr.At each wavelength, the major process is the rupture of a C-CH3 bond, which leads to the formation of methyl and CH2=C=CHCH2.The quantum yield for this process is 0.83 +/- 0.08 at 213.8 nm.The lifetime of the intermediate involved in this process is 20 ns at 184.9 nm.Similar quantities of ethylene and C3H4 (φ >/= 0.050) and propene and acetylene (φ >/= 0.023) are measured.All the measured yields decrease with an increase in the pressure.In addition to these fragmentation processes, isomerization reactions are also observed, particularly at 228.8 nm.They lead to the formation of 1,3- and 1,4-pentadiene as well as 3-methyl-1,2-butadiene.The Stern-Volmer plot for each isomer different and each plot shows a strong negative curvature, indicating the coplexity of the reaction process.The lifetime of each intermediate is 2 ns or less.
- Deslauriers, Helene,Dufour, Sylvain,Collin, Guy J.
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p. 1513 - 1519
(2007/10/02)
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- Isomerisation des radicaux insatures. III. Radicaux α,α,β-, α,β,γ- et α,α,γ-trimethallyles
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α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0-nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively.Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes.An internal sigmatropic 1,2-hydrogen atom transfer process is part of the proposed mechanism to explain such products.Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C-C) bond, then one β(C-H), and, to a lesser extent, one central C-CH3 bond.
- Deslauriers, Helene,Collin, Guy J.
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p. 3168 - 3173
(2007/10/02)
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- THE PHOTOLYSIS OF 2,3- AND 3,3-DIMETHYL-1-BUTENE AT 147.0 AND 184.9 nm
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The photofragmentation of 2,3-dimethylbutene and 3,3-dimethylbutene has been studied at 147 and 184.9 nm in the gas phase.The main primary decomposition process at both wavelengths involves the rupture of a β(C-C) bond.The quantum yield for this process is higher than 0.7 at 147 nm and is probably even higher at 184.9 nm.All dimethyallyl radicals formed at 147 nm in this process decompose at low pressure, but some of them isomerize from the α,β- to the α,α- structure (and vice versa) - via a 1,4-H transfer - before decomposition.At 184.9 nm, the same primary process is used to get a rough value for the lifetime of the photoexcited molecule, compared with the one made RRKM calculations by assuming that all the photon energy resides in the vibrational framework of the fundamental electronic state.These lifetimes are about one nanoseconde or less.
- Deslauriers, Helene,Collin, Guy J.
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- Gas-phase photolysis of spiropentane at 147.0 nm
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The gas-phase photolysis of spiropentane has been investigated using xenon (147.0 nm) resonance radiation.Major products observed in order of decreasing importance are ethylene, allene, methylacetylene, 1,2-butadiene, acetylene, propylene, and vinylacetylene.Nitric oxide was used as a radical scavenger while hydrogen sulfide and hydrogen iodide were employed as radical interceptors in the determination of the relative importance of radical and molecular processes, CH3/CH2 and CH3C. radicals were identified and quantified.Seven primary reaction channels were postulated of which those involving the "elimination" of ethylene were the most predominant accounting for 71percent of the photodecomposition.
- Paller, M.,Doepker, R. D.
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p. 3593 - 3596
(2007/10/02)
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- Thermal Rearrangements, part XIV. Gas Phase Kinetics of Pyrolysis of 1-Methyl-1-cyclopropene
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The title study has been carried out in the temperature range 210-250 deg C.The isomerisation products are butyne (91-94percent), 1,3-butadiene (5-8percent), and 1,2-butadiene (1-2percent).No other products were detected and material recovery was complete within experimental error (+/- 5percent).The reaction obeyed first-order kinetics, with the products formed by parallel pathways, and appeared to both unimolecular and homogeneous although some surface sensitivity was detected in packed vessels.Studies of pressure dependence showed characteristic rate constant "fall-off" below 20 Torr (SF6) and 100 Torr (N2).Within at least 2percent of the high pressure limit, the following Arrhenius equation for overall decomposition was found: log(k/s-1) = (12.91 +/- 0.15) - (160 +/- 1.5 kJ mol-1)/RTln 10.Arrhenius equations were similarly found for the individual pathways.The figures are discussed in the light of Transition State Theory and represent a significant improvement over a previous study.It is argued that all products arise via 1,2 shifts in a diradical-like intermediate and the propensities for different H shifts are discussed.A 1-methyl substituent, rather surprisingly, deactivates cyclopropene in its isomerisation reactions.
- Hopf, Henning,Wachholz, Gerhard,Walsh, Robin
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p. 3579 - 3587
(2007/10/02)
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- SYNTHESIS OF ISOCOUMARINS VIA THALLATION-OLEFINATION OF BENZOIC ACIDS
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Benzoic acid and substituted benzoic acids are readily thallated by thallium(III) trifluoroacetate and subsequently reacted with palladium chloride and simple olefins, allylic halides, vinyl halides, or vinyl esters to give isocoumarins.The organic halide reactions are catalytic in palladium. 1,2- and 1,3-dienes also react catalytically to afford 4-alkylidene- and 3-vinyl-3,4-dihydroisocoumarins, respectively.Vinylcyclopropanes also afford 3-vinyl-3,4-dihydroisocoumarins.This highly convenient thallation-olefination approach appears quite general for the synthesis of isocoumarins.
- Larock, R. C.,Varaprath, S.,Lau, H. H.,Fellows, C. A.
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p. 5274 - 5284
(2007/10/02)
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- Photocatalytic Hydrogenation of Alkynes and Alkenes with Water over TiO2. Hydrogenation Accompanied by Bond Fission
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Photocatalytic reactions of alkynes and alkenes with water have been investigated over TiO2 powder.The major photoformed products are those formed by hydrogenation accompained by C=C or CC bond fission.Oxidation products such as CO and CO2 are also formed.From the change in the product yields with the remaining amount of water adsorbed as well as the pressure of water vapor it is concluded that water molecules and not surface OH- groups are responsible for the reaction and also that vacant sites for the alkyne (or alkene) adsorption are necessary for the occurrence of the reaction.The fission of the C=C or CC bond observed with the hydrogenation is attributed to the interaction of the alkynes (or alkenes) with the trapped e-(Ti3+) and h+(.OH) pairs.It is suggested that a close association of photoformed electron and hole pairs plays a significant role in the bond fission.
- Anpo, Masakazu,Aikawa, Norikazu,Kodama, Sukeya,Kubokawa, Yutaka
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p. 2569 - 2572
(2007/10/02)
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- ISOMERIZATION OF BUTYNES TO 1,3-BUTADIENE OVER SOLID BASE CATALYSTS
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1-Butyne and 2-butyne underwent isomerization to 1,3-butadiene over CaO, SrO, MgO, La2O3, ThO2 and ZrO2 catalysts below 100 deg C.Among these catalysts, the CaO catalyst exhibited the highest activity, and was active even at 30 deg C.
- Sato, Kenji,Hattori, Hideshi
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p. 1881 - 1882
(2007/10/02)
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- Vacuum-ultraviolet (147.0 nm and 123.6 nm) photolysis of 1,1-dimethylcyclopropane
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The gas-phase photolysis of 1,1-dimethylcyclopropane has been investigated using xenon (147.0 nm) and krypton (123.6 nm) resonance radiation.Major products observed in order of decreasing importance were isobutene, ethylene, hydrogen, 1,3-butadiene, 2-methyl-1,3-butadiene, propylene, allene, methylacetylene, and acetylene.Radical scavengers, NO and O2, and radical interceptors, H2S/D2S and HI, were used to determine the relative importance of radical and molecular processes.CH3, C2H3, C3H5, and C4H7 radical species were identified and quantified.Ten primary reaction channels were postulated, of which the elimination of methylene was the most predominant, accounting for 34percent of the photo-decomposition at 147.0 nm and 39percent at 123.6 nm.Although ionization was established at 123.6 nm (η=0.10) the nature of a charge transfer of other ion-molecule reaction channel leading to the formation of 2-methyl-1-butene and 2-methyl-2-butene could not be determined.
- Binkewicz, Joseph B.,Kaplan, Michael,Doepker, Richard D.
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p. 537 - 542
(2007/10/02)
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