- Site-Selective N-Dealkylation of 1,2,3-Triazolium Salts: A Metal-Free Route to 1,5-Substituted 1,2,3-Triazoles and Related Bistriazoles
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N3-Alkylation of 1-(pivaloyloxymethyl)-1,2,3-triazoles with alkyl triflates carrying latent "click" functionality, followed by a nucleophile-promoted N1-dealkylation of the resulting strongly electrophilic intermediate triazolium salts, provides an efficient route to 1,5-disubstituted 1,2,3-triazoles. The azide and alkyne groups incorporated by N-alkylation can be submitted to further copper-catalyzed azide-alkyne and Huisgen cycloadditions to provide bis(1,2,3-triazoles) with unprecedented 1,5/1,4 substitution patterns.
- Monasterio, Zaira,Irastorza, Aitziber,Miranda, José I.,Aizpurua, Jesus M.
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supporting information
p. 2511 - 2514
(2016/06/09)
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- Synthesis of Diphenylchalcogenophene Diboronic Acid Bis(pinacol) Esters and Halogen Photoelimination from Tellurium by Triplet–Triplet Annihilation
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The synthesis of diphenylthiophene-, diphenylselenophene-, and diphenyltellurophene-based diboronic bis(pinacol) esters and their optoelectronic properties is reported. The addition of bromine to the borylated diaryltellurophene and subsequent photoelimination are investigated. The photochemical quantum yield of bromine photoelimination is (9.7±0.2) % at a 4.4 m trap (2,3-dimethyl-1,3-butadiene) concentration. It is found that the bromine photoelimination reaction can also be driven by the incorporation of a triplet sensitizer through a triplet–triplet annihilation process.
- Li, Peng-Fei,Carrera, Elisa I.,Seferos, Dwight S.
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p. 917 - 921
(2016/09/13)
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- Kinetics of the reactions of hydroxyl radicals with diacetylene and vinylacetylene
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Highly unsaturated hydrocarbons like diacetylene (C4H2) or vinylacetylene (C4H4) are important intermediates in combustion that can have impact on soot formation. One of their major loss channels is reaction with hydroxyl radicals (OH). We studied the reactions C4H2 + OH → products (1) and C4H4 + OH → products (2) in a quasi-static reactor with helium as bath gas. The hydroxyl radicals were produced by laser flash-photolysis of nitric acid at a wavelength of 248 nm and detected by laser-induced fluorescence with excitation at 282 nm. The rate coefficients were obtained from the intensity-time profiles under pseudo-first order conditions with respect to OH. We found a virtually temperature-independent rate coefficient for reaction (1): k1 = (1.0 ± 0.3) × 10-11 cm3 s-1 (T = 290-670 K, P = 2.7-30.5 bar) and a weakly negative temperature-dependent rate coefficient for reaction (2): k2(T) = (6.4 ± 1.9) × 10-12 exp (486 K/T) cm3 s-1 (T = 295-740 K, P = 1.7-19.2 bar). For neither of the two reactions pressure dependence was observed. From comparisons with analogous reaction systems, we conclude that the dominating reaction pathway is OH addition, where in the case of C4H4 the double bond is preferred over the triple bond.
- Sommerer, J?rg,Olzmann, Matthias
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p. 495 - 505
(2015/04/14)
-
- METHODS OF PRODUCING DICARBONYL COMPOUNDS
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Dicarboxylic acids, such as adipic acid, and diesters, such as adipates, may be produced by hydrogenating alkynes that may be produced from raw materials salvaged from waste stream processes. The carbons of the dicarboxylic acids are provided by alkynes generated from biomass waste and carbon dioxide recovered from waste streams such as exhaust gases.
- -
-
Paragraph 0038
(2015/05/06)
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- Formation of fulvene in the reaction of C2H with 1,3-butadiene
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Abstract Products formed in the reaction of C2H radicals with 1,3-butadiene at 4 Torr and 298 K are probed using photoionization time-of-flight mass spectrometry. The reaction takes place in a slow-flow reactor, and products are ionized by tunable vacuum-ultraviolet light from the Advanced Light Source. The principal reaction channel involves addition of the radical to one of the unsaturated sites of 1,3-butadiene, followed by H-loss to give isomers of C6H6. The photoionization spectrum of the C6H6 product indicates that fulvene is formed with a branching fraction of (57 ± 30)%. At least one more isomer is formed, which is likely to be one or more of 3,4-dimethylenecyclobut-1-ene, 3-methylene-1-penten-4-yne or 3-methyl-1,2-pentadien-4-yne. An experimental photoionization spectrum of 3,4-dimethylenecyclobut-1-ene and simulated photoionization spectra of 3-methylene-1-penten-4-yne and 3-methyl-1,2-pentadien-4-yne are used to fit the measured data and obtain maximum branching fractions of 74%, 24% and 31%, respectively, for these isomers. An upper limit of 45% is placed on the branching fraction for the sum of benzene and 1,3-hexadien-5-yne. The reactive potential energy surface is also investigated computationally. Minima and first-order saddle-points on several possible reaction pathways to fulvene + H and 3,4-dimethylenecyclobut-1-ene + H products are calculated.
- Lockyear, Jessica F.,Fournier, Martin,Sims, Ian R.,Guillemin, Jean-Claude,Taatjes, Craig A.,Osborn, David L.,Leone, Stephen R.
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p. 232 - 245
(2015/04/14)
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- Electronic coupling mediated by furan, thiophene, selenophene and tellurophene in a homologous series of organic mixed valence compounds
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Charge delocalization in the mixed-valent monocationic forms of phenothiazine-decorated chalcogenophenes is explored by cyclic voltammetry, optical absorption and EPR spectroscopy. Single units of furan, thiophene, selenophene and tellurophene are found to mediate electronic coupling between the phenothiazines attached to their 2- and 5-positions roughly equally well. Electronic communication seems to occur mostly through the butadiene-like backbone of the chalcogenophenes. the Partner Organisations 2014.
- Jahnke, Ann Christin,Spulber, Mariana,Neuburger, Markus,Palivan, Cornelia G.,Wenger, Oliver S.
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supporting information
p. 10883 - 10886
(2014/10/15)
-
- Partially oxidized gold nanoparticles: A catalytic base-free system for the aerobic homocoupling of alkynes
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The mechanism of alkyne homocoupling over gold nanoparticles and clusters, isolated and supported on CeO2, has been theoretically investigated by means of periodic DFT calculations. The theoretical study indicates that O2 dissociation on gold generates basic O atoms able to abstract the proton of the alkyne, and cationic Auδ+ and Au+ species that decrease the activation barrier for the CC bond forming step. Kinetic results show that the base-free homocoupling of alkynes is effectively catalyzed by gold nanoparticles supported on different solids, and confirm the theoretical prediction that the dissociation of oxygen on the gold nanoparticle is the controlling step of the global reaction.
- Boronat, Mercedes,Laursen, Siris,Leyva-Perez, Antonio,Oliver-Meseguer, Judit,Combita, Diego,Corma, Avelino
-
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- Pyridyl-and pyridylperoxy radicals-a matrix isolation study
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The three isomeric pyridyl radicals 2a-c were synthesised using flash vacuum pyrolysis in combination with matrix isolation and characterised by infrared spectroscopy. The IR spectra are in good agreement with spectra calculated using density functional theory methods. The reaction of the pyridyl radicals 2 with molecular oxygen leads to the formation of the corresponding pyridylperoxy radicals 3a-c. The peroxy radicals 3 are photolabile, and irradiation results in syn-anti isomerisation of 3a and 3b and ring expansion of all three isomers of 3.
- Korte, Andre,Mardyukov, Artur,Sander, Wolfram
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p. 1324 - 1329
(2014/11/07)
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- A novel tellurophene-containing conjugated polymer with a dithiophenyl diketopyrrolopyrrole unit for use in organic thin film transistors
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A new tellurophene-based π-conjugated polymer, PDTDPPTe, was synthesized. PDTDPPTe exhibits a smaller optical band gap (Eg opt = 1.25 eV) than thiophene-based PDTDPPT (Eg opt = 1.30 eV). Thin-film transistors comprising PDTDPPTe displayed outstanding performance (μmax = 1.78 cm2 V-1 s-1, Ion/Ioff = 105-6).
- Kaur, Matinder,Seul Yang, Da,Shin, Jicheol,Wan Lee, Tae,Choi, Kihang,Ju Cho, Min,Hoon Choi, Dong
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supporting information
p. 5495 - 5497
(2013/06/27)
-
- Reaction rate and isomer-specific product branching ratios of C 2H + C4H8: 1-butene, cis -2-butene, trans -2-butene, and isobutene at 79 K
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The reactions of C2H radicals with C4H8 isomers 1-butene, cis-2-butene, trans-2-butene, and isobutene are studied by laser photolysis-vacuum ultraviolet mass spectrometry in a Laval nozzle expansion at 79 K. Bimolecular-reaction rate constants are obtained by measuring the formation rate of the reaction product species as a function of the reactant density under pseudo-first-order conditions. The rate constants are (1.9 ± 0.5) × 10-10, (1.7 ± 0.5) × 10 -10, (2.1 ± 0.7) × 10-10, and (1.8 ± 0.9) × 10-10 cm3 s-1 for the reaction of C2H with 1-butene, cis-2-butene, trans-2-butene, and isobutene, respectively. Bimolecular rate constants for 1-butene and isobutene compare well to values measured previously at 103 K using C2H chemiluminescence. Photoionization spectra of the reaction products are measured and fitted to ionization spectra of the contributing isomers. In conjunction with absolute-ionization cross sections, these fits provide isomer-resolved product branching fractions. The reaction between C2H and 1-butene yields (65 ± 10)% C4H4 in the form of vinylacetylene and (35 ± 10)% C5H6 in the form of 4-penten-1-yne. The cis-2-butene and trans-2-butene reactions yield solely 3-penten-1-yne, and no discrimination is made between cis- and trans-3-penten-1-yne. Last, the isobutene reaction yields (26 ± 15)% 3-penten-1-yne, (35 ± 15)% 2-methyl-1-buten-3-yne, and (39 ± 15)% 4-methyl-3-penten-1-yne. The branching fractions reported for the C2H and butene reactions indicate that these reactions preferentially proceed via CH3 or C2H3 elimination rather than H-atom elimination. Within the experimental uncertainties, no evidence is found for the formation of cyclic species.
- Bouwman, Jordy,Fournier, Martin,Sims, Ian R.,Leone, Stephen R.,Wilson, Kevin R.
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p. 5093 - 5105
(2013/07/25)
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- Bimolecular rate constant and product branching ratio measurements for the reaction of C2H with ethene and propene at 79 K
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The reactions of the ethynyl radical (C2H) with ethene (C 2H4) and propene (C3H6) are studied under low temperature conditions (79 K) in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by 193 nm photolysis of acetylene (C 2H2) and the reactions are studied in nitrogen as a carrier gas. Reaction products are sampled and subsequently photoionized by the tunable vacuum ultraviolet radiation of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The product ions are detected mass selectively and time-resolved by a quadrupole mass spectrometer. Bimolecular rate coefficients are determined under pseudo-first-order conditions, yielding values in good agreement with previous measurements. Photoionization spectra are measured by scanning the ALS photon energy while detecting the ionized reaction products. Analysis of the photoionization spectra yields-for the first time-low temperature isomer resolved product branching ratios. The reaction between C2H and ethene is found to proceed by H-loss and yields 100% vinylacetylene. The reaction between C2H and propene results in (85 ± 10)% C4H4 (m/z = 52) via CH3-loss and (15 ± 10)% C5H6 (m/z = 66) by H-loss. The C 4H4 channel is found to consist of 100% vinylacetylene. For the C5H6 channel, analysis of the photoionization spectrum reveals that (62 ± 16)% is in the form of 4-penten-1-yne, (27 ± 8)% is in the form of cis-and trans-3-penten-1-yne and (11 ± 10)% is in the form of 2-methyl-1-buten-3-yne.
- Bouwman, Jordy,Goulay, Fabien,Leone, Stephen R.,Wilson, Kevin R.
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experimental part
p. 3907 - 3917
(2012/07/02)
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- UV laser photodeposition of nanomagnetic soot from gaseous benzene and acetonitrile-benzene mixture
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Megawatt KrF laser gas-phase photolysis of benzene and acetonitrile-benzene mixture was studied by using mass spectroscopy-gas-chromatography and Fourier transform infrared spectroscopy for analyses of volatile products, and by Fourier transform infrared, Raman and X-ray photoelectron spectroscopy, electron microscopy and magnetization measurements for analyses of solid products deposited from the gas-phase. The results are consistent with carbonization of benzene and decomposition of non-absorbing acetonitrile in carbonizing benzene through collisions with excited benzene and/or its fragments. The solid products from benzene and acetonitrile-benzene mixture have large surface area and are characterized as nanomagnetic amorphous carbonaceous soot containing unsaturated C centers prone to oxidation. The nanosoot from acetonitrile-benzene mixture incorporates CN groups, confirms reactions of benzene fragments with CN radical and has a potential for modification by reactions at the CN bonds.
- Pola, Josef,Ouchi, Akihiko,Mary?ko,Vorlí?ek,?ubrt, Jan,Bakardjieva,Bastl, Zdeněk
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experimental part
p. 188 - 194
(2012/02/02)
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- Manganese-catalyzed oxidative homo-coupling of aryl Grignard chlorides
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Manganese-catalyzed homo-coupling of aryl magnesium chlorides to give biphenyls was successfully achieved using manganese chloride as catalyst. A variety of aryl magnesium chlorides were efficiently converted into the corresponding symmetrical biaryls using 10 mol% MnCl2 as catalyst in the presence of a stoichiometric amount of 1,2-dichloroethane. Since the aryl chlorides, from which the Grignard reagents were prepared, are cheaper and more readily available that the corresponding bromides and iodides this procedure should become the method of choice for preparing symmetrical biaryls.
- Zhou, Zhiming,Xue, Weizhe
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supporting information; experimental part
p. 599 - 603
(2009/05/30)
-
- A modified synthesis of tellurophene using NaBH4 to generate sodium telluride
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A modified synthesis of tellurophene by reaction of diacetylene with sodium telluride is described. The primary modification involves the convenient in situ generation of sodium telluride by reduction of tellurium metal with NaBH4 in water.
- Sweat, Daniel P.,Stephens, Chad E.
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p. 2463 - 2464
(2008/09/20)
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- Total synthesis of 1-(Z)-atractylodinol
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The total synthesis of 1-(Z)-atractylodinol, a natural polyacetylenic alcohol with several biological activities, has been achieved using a newly developed telluride synthon and a novel use for the Negishi type coupling reaction employing vinyl tellurides.
- Oliveira, Juliana M.,Zeni, Gilson,Malvestiti, Ivani,Menezes, Paulo H.
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p. 8183 - 8185
(2007/10/03)
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- Low temperature NH(X 3Σ-) radical reactions with NO, saturated, and unsaturated hydrocarbons studied in a pulsed supersonic Laval nozzle flow reactor between 53 and 188 K
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The reactions of ground-state imidogen radicals (NH(X 3Σ -)) with NO and select saturated and unsaturated hydrocarbons have been measured in a pulsed supersonic expansion Laval nozzle flow reactor in the temperature range 53-188 K. The rate coefficients for the NH + NO system display negative temperature dependence in the temperature regime currently investigated and a global temperature-dependent fit is best represented in a modified power law functional form, with k1(NH + NO) = (4.11 ± 0.31) × 10-11 × (T/300)(-0.30±0.17) × exp(77±21/T) cm3/s. The reactions of NH with ethylene, acetylene, propene, and diacetylene were measured over the temperature range 53-135 K. In addition, the reactions of NH with methane and ethane were also measured at 53 K, for reasons discussed later. The temperature dependence of the reactions of NH with the unsaturated hydrocarbons are fit using power law expressions, k(T) = A(T/300)-n, and are as follows: k4, = (2.3 ± 1.2) × 10-12 × (T/300)(-1.09±0.333) cm3/s, k5 = (4.5 ± 0.3) × 10-12 × (T/300) (-1.07±0.04) cm3/s, k6 = (5.6 ± 1.9) × 10-12 × (T/300)(-1.23±0.21) cm3/s, and k7 = (7.4 ± 1.8) × 10 -12 × (T/300)(-1.23±0.15) cm3/s for ethylene, acetylene, propene, and diacetylene, respectively. The rate for NH + ethane at 53 K is measured to be k3 = (6.8 ± 1.7) × 10-12 cm3/s, while that for methane at the same temperature represents an upper bound of k2 ≤ (1.1 ± 4.3) × 10-12 cm3/s, as this is at the limits of measurement with our current technique. The behavior of these systems throughout the temperature range explored indicates that these reactions occur over a potential energy surface without an appreciable barrier through a complex formation mechanism. Implications for chemistry in low temperature environments where these species are found are briefly discussed.
- Mullen, Christopher,Smith, Mark A.
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p. 1391 - 1399
(2007/10/03)
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- Acetaldehyde dehydration to produce ethyne
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A process to produce ethyne comprising passing acetaldehyde in the gas phase through a reaction zone containing a dehydrating metal oxide catalyst such as aluminum oxide or magnesium oxide at a temperature of approximately 375 C. to produce ethyne and water and a cooling zone following the reaction zone. This method having the advantage of ease of separation of ethyne from the co-product water and unreacted acetaldehyde by simple condensation whereby the acetaldehyde and water liquify while The ethyne remains gaseous.
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-
-
- 3,5-Pyridyne-A Heterocyclic meta-Benzyne Derivative
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3,5-Pyridyne (3) has been generated by flash vacuum pyrolysis of 3,5-diiodopyridine (20) and 3,5-dinitropyridine (21) and characterized by IR spectroscopy in cryogenic argon matrices. The aryne can clearly be distinguished from other side products by its photolability at 254 nm, inducing a rapid ring-opening presumably to (Z)-1-aza-hex-3-ene-1,5-diyne. As byproducts of the pyrolysis, HCN and butadiyne were identified, together with traces of acetylene, cyanoacetylene, (E)-1-aza-hex-3-ene-1,5-diyne, and the 3-iodo-5-pyridyl radical (from 20). Several pathways for rearrangements and fragmentations of 3 and of the parent meta-benzyne (1) have been explored computationally by density functional theory and ab initio quantum chemical methods. The lowest energy decomposition pathway of biradicals 1 and 3 is a ring-opening process accompanied by hydrogen migration, leading to (Z)-hex-3-ene-1,5-diyne [(Z)-10] and (Z)-3-aza-hex-3-ene-1,5-diyne [(Z)-24], respectively. Both reactions require activation energies of 45-50 kcal mol -1. Mechanisms leading from (Z)-24 or directly from 3 to the experimentally observed byproducts are discussed. Upon replacement of the C(5)H moiety by N in meta-benzyne, high-level calculations predict a modest shortening of the interradical distance by 5-7 pm and a reduction of the singlet-triplet energy splitting by 3 kcal mol-1, in good agreement with isodesmic equations, according to which the singlet ground state of 3 is destabilized relative to 1 by 3-4 kcal mol-1. In contrast to 3,5-borabenzyne (2), which is found to be doubly aromatic, nucleus-independent chemical shifts of 3 are almost identical to that of pyridine, indicating the absence of paramagnetic ring current effects that may be associated with in-plane antiaromaticity . As compared with 1, the overall perturbation caused by the nitrogen atom in 3 is weak, and four electron, three center interaction is of minor importance in this molecule.
- Winkler, Michael,Cakir, Bayram,Sander, Wolfram
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p. 6135 - 6149
(2007/10/03)
-
- Submerged electric arc between graphite electrodes: A one-pot tool for the synthesis of long-chain polyynes in solution
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Polyynes, a class of molecules described by the general formula H-(CC) mH (where m is an integer) can be synthesized using an electric arc between graphite electrodes submerged in an organic solvent such as methanol, n-hexane, n-dodecane, decahydronaphthalene or acetonitrile. When the electric arc is used in acetonitrile at -40°C, polyyne chains of up to 18 carbon atoms (m=9) have been produced together with monocyanopolyyne as by-product. The polyynes can be reduced to ene-ynes by shaking a hexane solution of them with Zn/HCl.
- Cataldo, Franco
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p. 141 - 144
(2007/10/03)
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- Perthio- and perseleno-1,3-butadienes, -but-1-ene-3-ynes, and -[3]-cumulenes: One-step syntheses from 1,4-dilithio-1,3-butadiyne
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(Matrix presented) Treatment of 1,4-dilithio-1,3-butadiyne (1) with dichalcogenides RSSR or RSeSeR affords dithio- and diseleno-1,3-butadiynes (2, 3), perthio- and perseleno-[3]-cumulenes (4, 5), perthio- and perseleno-1,3-butadienes (6, 7), and/or perthio- and perseleno-but-1-ene-3-ynes (8, 9). The products can be controlled by stoichiometry and temperature, by the presence or absence of oxygen, and by choice of the "R" group. By X-ray crystallography, hexa(methylthio)-1,3-butadiene is highly twisted, with a torsion angle [Φ(CCCC)] of 84.7° and an elongated C(2)-C(3) distance of 1.484(3) A.
- Block, Eric,Tries, Frank,He, Chunhong,Guo, Chuangxing,Thiruvazhi, Mohan,Toscano, Paul J.
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p. 1325 - 1327
(2007/10/03)
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- Synthesis and properties of novel medium-sized heterocyclic compounds containing two sulfur atoms in the ring and synthetic approaches to conjugated cyclic disulfonium ylides
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Tribenzo[bf,h][1,4]dithiecin (8) was prepared by coupling 2,2'- bis(bromomethyl)biphenyl (10) with 1,2-benzenedithiol (11) in the presence of Nail in acetonitrile. Another novel dithiecin derivative, 1,8-dihydro-2,7benzodithiecin (9) was synthesized by coupling of 1,4-dimercapto-2,3-Oisopropylidene-Lg-threitol (13a) with α,α'-dibromo-o-xylene (12), followed by hydrolysis and subsequent dehydration via the mesylate derivative (16). The benzodithiecin (9) was also prepared by treatment of dithiol (18) with butadiyne along with α,α'-bis(1-buten-3-ynylthio)-o-xylene (19) as a byproduct. Compound (19) was subjected to an intramolecular coupling reaction using CuCl-pyridine-O2 in benzene to yield the 12-membered ring compound (23). We also describe our effort to prepare the corresponding cyclic diylide compounds from the above new dithiecins (8) and (9), and known dithiecin (7).
- Shimizu, Hiroshi,Watanabe, Hiroyoshi,Mizuno, Masahiro,Kataoka, Tadashi,Hori, Mikio
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p. 139 - 150
(2007/10/03)
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- Diacetylene ω-Glycols. Etherates - Adducts of 1,6-di(p-Halogeno)-1,6-diphenylhexa-2,4-diyne-1,6-diols with Diethyl Ether and Dioxane
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Stable, crystalline adducts of the title diols Z(F, Cl, Br, I) with diethyl ether and dioxane have been obtained. Spectral properties have been described. No formation of etherates from tetraphenyl diols not containing halogen atoms (1) has been found.
- Jasiobedzki, Wieslaw,Moszczynski-Petkowski, Rafal,Wozniak-Kornacka, Janina
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p. 225 - 234
(2007/10/03)
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- A detailed numerical study of the evolution of soot particle size distributions in laminar premixed flames
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In this work, two numerical techniques, viz. the method of moments and a discrete h-p-Galerkin method, have been applied for numerical simulation of soot formation in a laminar premixed acetylene/oxygen/argon flame. From the evolution of the PAH and the soot particle size distributions, new insight into the different processes of soot formation is provided. For this, the single submodels have been examined with respect to their influence on the PAH and the soot particle size distributions. The particle inception step was studied in detail by comparing the simulated PAH size distributions with experimental results. Additionally, an estimation of the interaction energy of layered PAH dimers was performed by quantum chemical calculations. From these results, some evidence for the particle inception model employing coalescence of PAH molecules has been found. The numerical results for the gas phase chemical species, the particle number densities and volume fractions of soot as well as for the soot particle size distributions are compared with experimental data. Thereby, the consistency of the entire model is demonstrated.
- Appel, Joerg,Bockhorn, Henning,Wulkow, Michael
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p. 635 - 645
(2007/10/03)
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- Polyphospha[m]cyclo[n]carbons (m+n = 15, 20, 25, 30, 40)
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The Eglinton reaction of diethynyl(2,4,6-tri-tert-butylphenyl)phosphane (7a), that is, the oxidative coupling of 3, 4, 5, or 6 of these phosphane units, affords a mixture of the 15-, 20-, 25-, and 30-membered macrocycles 8, 9, 10, and 11. Pure triphosphacyclopentadecahexayne 8 and pentaphosphacyclopentacosadecayne 10 were isolated by HPLC, while the mixture of 9 and 11 could not be separated. Multistep syntheses of open-chain polyphosphapolyynes are described, whose intra- or intermolecular coupling yields the phosphamacrocycles 8, 9, and 11. Eglinton coupling of bis(ethynylphosphanyl)butadiyne (17) gave a mixture of the 20-membered tetraphosphacycloicosaoctayne 9, the 30-membered hexaphosphacyclotriacontadodecayne 11, and the 40-membered octaphosphacyclotetracontahexadecayne 23 as result of a di-, tri-, and tetramerization, respectively. Intramolecular coupling of bis[(ethynylphosphanyl)butadiynyl]phosphane 25a gave 8, while intermolecular coupling gave 11; these two compounds were isolated by chromatography to give yields of 70 and 5%, respectively. The open-chain tetraphosphaeikosaoctayne 28 couples intramolecularly to give 9 and intermolecularly to give the 40-membered octaphosphacyclotetracontahexadecayne 23, which was isolated in the pure form. Octaphosphatetracontahexadecayne 32 cyclized to give 23, exclusively. The temperature-dependent 1H and 31p NMR spectra of the open-chain and cyclic ethynylphosphanes indicated a lowering of the inversion barrier of the tertiary phosphanes from the usual 130-140 kJmo1-1 to 65-75 kJmo1-1. Ab initio calculations proved that the dramatic reduction of the inversion barriers results from the interaction of the lone pair on phosphorus with the π orbitals of the triple bonds in the planar transition state during inversion. The situation is comparable with the dramatic reduction of the P inversion barrier in phospholes, because of the planar, aromatic transition state. The polyphospha[m]cyclo[n]carbons may be considered as precursors to cyclic P(m)C(n) systems.
- Maerkl, Gottfried,Zollitsch, Thomas,Kreitmeier, Peter,Prinzhorn, Michael,Reithinger, Sabine,Eibler, Ernst
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p. 3806 - 3820
(2007/10/03)
-
- A selected ion flow tube study of the reactions of small CmHn+ ions with O atoms
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The reactions of thirteen CmHn+ ions (m ≤ 6) with atomic and molecular oxygen and nitric oxide have been measured using a selected ion flow tube operating at room temperature. Rate coefficients and product distributions are reported for each reaction. Most of the hydrocarbon ions studied exhibit relatively rapid reactions with O atoms and proceed at substantial fractions of the collision rate. All O atom reactions showed multiple product channels and the formation of a -C-O bond, either in the ion product or the neutral product of reaction.
- Scott, Graham B.I.,Milligan, Daniel B.,Fairley, David A.,Freeman, Colin G.,McEwan, Murray J.
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p. 4959 - 4965
(2007/10/03)
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- ArF and KrF lasers-induced gas-phase photolysis of selenophene and telluropllene: Extrusion of Te and Se and intramolecular 1,3-H shift competing with β-C-C cleavage in C4H4 residue
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ArF (193 nm) and KrF (248 nm) laser-induced photolysis of gaseous selenophene and tellurophene (C4H4M, M = Se and Te) has been examined. It is shown that, unlike thiophene and furan, selenophene and tellurophene cleave both M-C bonds and yield the elemental heteroatom (Se, Te), 1-buten-3- yne, and ethyne. The proposed mechanism involves an intermediate ·HC=CH- CH=CH· diradical that decomposes via two competitive pathways, namely, 1,3-H shift to 1-buten-3-yne and/β-cleavage to two molecules of ethyne. It is shown that the relative importance of the channels depends both on the energy of the photon and on the heteroatom. Specifically, the 1,3-H shift/β- cleavage ratios are 2.3 (193 nm, M = Se), 3.6 (248 nm, M = Se), 1.4 (193 nm, M = Te), and 10.5 (248 nm, M = Te). The inertness of the Te residuum and the high preference for the 1,3-H shift in KrF laser photolysis of tellurophene suggest that this photolysis can serve as a source of the C4H4 diradical for mechanistic studies.
- Pola, Josef,Ouchi, Akihiko
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p. 2759 - 2762
(2007/10/03)
-
- Synthesis of deuterated volatile lipid degradation products to be used as internal standards in isotope dilution assays. 1. Aldehydes
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The isotopically labeled compounds [5,6-2H2]hexanal (d-I), [2,3-2H2]-(E)-2-nonenal (d-II), [3,4-2H2]-(E,E)-2,4-nonadienal (d-III), and [3,4-2H2]-(E,E)-2,4-decadienal (d-IV) were prepared in good yields using new or improved synthesis procedures. Labeling position, chemical purity, and isotopic distribution of the compounds were characterized by various MS and NMR techniques. These molecules are used as internal standards in quantification experiments based on isotope dilution assay. Synthesis of d-I, d-III, and d-IV has not yet been reported in the literature.
- Lin, Jianming,Welti, Dieter H.,Arce Vera, Francia,Fay, Laurent B.,Blank, Imre
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p. 2813 - 2821
(2007/10/03)
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- Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices
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Irradiation of acetylene (4) in an argon matrix with an ArF laser (λ = 193 nm) yields the ethynyl radical C2H (5) and C2 (6). If the same wavelength is used to irradiate 4 in a xenon matrix, only the infrared signal of the compound Xe-C2 (7) can be detected. The same band is found on irradiation at λ = 248 nm (KrF laser) in a xenon matrix, despite the fact that acetylene (4) does not absorb light of this wavelength. Irradiation of the T-shaped acetylene dimer 9 in an argon or xenon matrix at λ = 193 nm yields butadiyne (11) and vinylacetylene (12). However, irradiation with a KrF laser (λ = 248 nm) in a xenon matrix additionally yields cyclobutadiene (13). The dependence of the mechanisms of the fragmentation and dimerization of acetylene (4) on the matrix material is discussed.
- Maier, Günther,Lautz, Christian
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p. 769 - 776
(2007/10/03)
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- Radical pathways in the thermal decomposition of pyridine and diazines: A laser pyrolysis and semi-empirical study
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The mechanisms of thermal decomposition of pyridine and the three isomeric diazines have been investigated by IR laser pyrolysis in conjunction with stable end-product analysis by FTIR, NMR and GC-MS, and radical detection by EPR spectroscopy. Calculations at semi-empirical and ab initio levels have provided confirmation of potential reaction pathways. For pyridine, reaction is initiated by formation of pyridyl radicals, as indicated by extensive isotope exchange with added deuterium. Experiments with bromopyridines show that open chain radicals arising from ring opening of 2-pyridyl and 3-pyridyl radicals each lead to stable gaseous products, while 4-pyridyl radicals produce solid deposits, and may be the principal agents in soot formation. The evidence suggests that 1,2-diazine decomposes via a molecular route leading to stoichiometric production of HCN and C2H2, while 1,3- and 1,4-diazine follow a pattern of H loss and ring radical opening analogous to that of pyridine.
- Hore, Nathan R.,Russell, Douglas K.
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p. 269 - 275
(2007/10/03)
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- Thermal decomposition of quinoline and isoquinoline. The role of 1-indene imine radical
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The thermal reactions of quinoline and isoquinoline were studied behind reflected shock waves in a pressurized driver single pulse shock tube over the temperature range 1275-1700 K and densities of ~3 ×10-5 mol/ cm3. The decomposition products found in the postshock mixtures of quinoline and isoquinoline and their production rates were identical for both isomers. They were C2H2, C6H5CN, HC≡CCN, C6H6, HCN, C6H5-C≡CH and C4H2. Trace quantities of C6H4, C5H5N and C5H4N-C≡CH were also found. The total disappearance rates of quinoline and isoquinoline are the same, and in terms of a first-order rate constant they are given by ktotal = 1013.0exp(-75.5 × 103/RT) s-1 where R is expressed in units of cal/(K mol). The same product distribution in the two isomers can be accounted for if the production of 1-indene imine radical as an intermediate is assumed. A kinetic scheme containing the reactions of both quinoline and isoquinoline with 72 species and 148 elementary reactions accounts for the observed product distribution. The reaction scheme is given, and the results of computer simulation and sensitivity analysis are shown.
- Laskin, Alexander,Lifshitz, Assa
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p. 928 - 946
(2007/10/03)
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- Silylenes of the elemental composition C4H2Si: Generation and matrix-spectroscopic identification
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Flash pyrolysis of 1,1-diethynyl-2,2,2-trimethyldisilane (16) and triethynylsilane (18) led to the formation of two silylenes of the elemental composition C4H2Si, namely diethynylsilylene (10) and ethynylsilacyclopropenylidene (7), which were isolated in an argon matrix at 10 K. Both compounds could be photoconverted into another isomer, butadiynylsilylene (9). The identification of these reactive intermediates is based on the comparison between the experimental and calculated IR spectra for the parent compounds as well as for their dideuterated and fully 13C-labeled isotopomers.
- Maier, Guenther,Reisenauer, Hans Peter,Meudt, Andreas
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p. 1285 - 1290
(2007/10/03)
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- (1Z,3Z)-Buta-1,3-dienyl-1-lithium species and substituted tellurophenes by Te/Li exchange on (1Z,3Z)-butyltelluro-1,3-butadienes and (1Z,3Z)-1,4-bis(butyltelluro)-1,3-butadienes
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(1Z,3Z)-1-Butyltelluro-1,3-butadienes 8, 9 and 12 obtained by the hydrotelluration of but-1-en-3-ynes 1, 2 and 5 were transformed into the corresponding buta-1,3-dienyl-1-lithium by reaction with n-BuLi. 1,3-Butadienes 14, 15, 17-20 were obtained with retention of the double bond geometry by reaction of the butadienyllithium intermediates with electrophiles. The butadienyllithium 13 obtained by the Te/Li exchange reaction in the (1Z,3Z)-1-butyltelluro-4-methoxy-1,3-butadiene 8 was reacted with benzaldehyde to form the corresponding alcohol 15 with total retention of configuration, that undergoes hydrolysis resulting into the (E,E)-5-phenyl-2,3-pentadien-1-al 16. Hydrotelluration of the 1-butyltellurobut-1-en-3-yne 3 permits the synthesis of the (1Z,3Z)-1,4-bis(butyltelluro)-1,3-butadiene 10 which undergoes cyclization, leading to substituted tellurophenes 24, 25, 27-29 via a sequential Csp2-Te and Csp3-Te bonds cleavage on reaction with n-BuLi followed by addition of electrophiles.
- Dabdoub, Miguel J.,Dabdoub, Vania B.,Guerrero Jr., Palimecio G.,Silveira, Claudio C.
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p. 4199 - 4218
(2007/10/03)
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- Enantioselective synthesis of haminol-1, an alarm pheromone of a Mediterranean mollusc
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The first enantioselective synthesis of (-)-(R)-haminol-1 is described in this paper. The chiral part of the molecule was prepared by reduction of an optically active β-ketosulfoxide. The all-trans trienic part was stereoselectively synthesized via reductive elimination of a 1,6-dibenzoate-2,4-diene with sodium amalgam.
- Solladie, Guy,Somny, Frederic,Colobert, Francoise
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p. 801 - 810
(2007/10/03)
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- Crossed beam reaction of atomic carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2): Observation of diacetylene, C4H2(X 1Σg+)
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The reaction of ground-state carbon, C(3Pj), with the propargyl radical, C3H3(X 2B2), is investigated at an average collision energy of 42.0 kJmol-1 employing the crossed molecular beams technique and a universal mass spectrometric detector. The laboratory angular distribution and time-of-flight spectra of the C4H2 product are recorded at mle=50. Forward-convolution fitting of our data reveals the formation of diacetylene, HCCCCH, in its X1Σg+ electronic ground state. The reaction dynamics are governed by an initial attack of C(3Pj) to the π-electron density at the acetylenic carbon atom of the propargyl radical, followed by a [1,2]-hydrogen migration to the n-C4H3 isomer. A final carbon-hydrogen bond rupture yields atomic hydrogen and diacetylene through a tight exit transition state located 30-60 kJmol-1 above the products. This first successful crossed molecular beams study of a reaction between an atom and a free radical marks the beginning of the next generation of crossed beams experiments elucidating the formation of molecular species in combustion processes, chemical vapor deposition, in the interstellar medium, outflows of carbon stars, and hydrocarbon-rich planetary atmospheres via radical-radical reactions.
- Kaiser,Sun,Suits,Lee
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p. 8713 - 8716
(2007/10/03)
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- Isomerization and decomposition of indole. Experimental results and kinetic modeling
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The thermal reactions of indole were studied in a pressurized driver single-pulse shock tube. Three isomerization products are obtained such as benzyl cyanide, o- and m-tolunitriles as a result of the pyrrole ring opening. The mechanism of indole-tolunitrile isomerization involves a series of unimolecular steps which are preceded by the very fast indole-indolenine tautomerism. The thermal decomposition of indole is initiated by H-atom ejection from the reactant. 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 pyrrole and indole are discussed.
- Laskin,Lifshitz
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p. 7787 - 7801
(2007/10/03)
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- Enantioselective synthesis of (+)-isobretonin A
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An enantioselective synthesis of (±)-isobretonin A is described. The chiral glycerol moiety was enantioselectively prepared by reduction of an optically active β-keto sulfoxide. The all-trans trienic part of the molecule was stereoselectively synthesized via reductive elimination of a 1,6-dibenzoate 2,4-diene with sodium amalgam.
- Solladie, Guy,Adamy, Marc,Colobert, Francoise
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p. 4369 - 4373
(2007/10/03)
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- Reaction rates of the CN radical with diacetylene and dicyanoacetylene
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Rates of CN reactions with diacetylene (DA) and dicyanoacetylene (DCA) have been measured at room temperature from the decay of the CN radical at various sample pressures by laser induced fluorescence. The rate constants are (4.2 ± 0.2) × 10-10 and (5.4±0.2) × 10-13 in units of cm3 molec-1 s-1 for DA and DCA, respectively, which follow the general pattern of CN reactions with hydrocarbons and nitriles. In the lower temperature circumstellar envelopes and Titan's atmosphere, the CN reaction with C4H2 may be more important, while the reaction with C4N2 may become less important.
- Seki, Kanekazu,Yagi, Mikio,He, Maoqi,Halpern, Joshua B.,Okabe, Hideo
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p. 657 - 662
(2007/10/03)
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- Low-temperature rate coefficients of C2H with CH4 and CD4 from 154 to 359 K
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Rate coefficients for the reaction C2H + CH4 → C2H2 + CH3 and C2H + CD4 → C2HD + CD3 are measured over the temperature range 154-359 K using transient infrared laser absorption spectroscopy. Ethyl radicals are produced by pulsed the laser photolysis of C2H2 in a variable temperature flow cell, and a tunable color center laser probes the transient removal of C2H (X2Σ+ (0,0,0)) in absorption. The rate coefficients for the reactions of C2H with CH4 and CD4 both show a positive temperature dependence over the range 154-359 K, which can be expressed as kCH(4) = (1.2±0.1) × 10-11 exp[(-149±12)/T] and kCD(4) = (8.7±1.8) × 10-12 exp[(-650±61)/T] cm3 molecule-1 s-1, respectively. The reaction of C2H + CH4 exhibits a significant kinetic isotope effect at 300 K of kCH(4)/kCD(4) = 2.5±0.2. Temperature dependent rate constants for C2H + C2H2 were also remeasured over an increased temperature range from 143 to 359 K and found to show a slight negative temperature dependence, which can be expressed as kC(2)H(2) = 8.6 × 10-16 T1.8 exp[(474±90)/T] cm3 molecule-1 s-1.
- Opansky,Leone
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p. 4888 - 4892
(2007/10/03)
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- Small rings, 91: Fragmentation of cyclobutane in a bromine-doped and undoped xenon matrix
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Irradiation (λ = 254 nm) of cyclobutane in a bromine-doped xenon matrix leads to ring opening in spite of the fact that cyclobutane does not absorb in this region. The main products are ethene and 1-butene. The same reaction, but less effectively, occurs upon irradiation with a laser (KrF laser, λ = 248 nm) in the absence of the halogen. The difference in the mechanisms of the two fragmentations is discussed. VCH Verlagsgesellschaft mbH, 1996.
- Maier, Guenther,Senger, Stefan
-
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- Shock tube and modeling study of 1,3-butadiene pyrolysis
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1,3-Butadiene (1,3-C4H6) was heated behind reflected shock waves over the temperature range of 1200-1700 K and the total density range of 1.3 × 10-5-2.9 × 10-5 mol/cm3. Reaction products were analyzed by gas-chromatography. The concentration change of 1,3-butadiene was followed by UV kinetic absorption spectroscopy at 230 nm and by quadrupole mass spectrometry. The major products were C2H2, C2H4, C4H4, and CH4. The yield of CH4 for a 0.5% 1,3-C4H6 in Ar mixture was more than 10% of the initial 1,3-C4H6 concentration above 1500 K. In order to interpret the formation of CH4 successfully, it was necessary to include the isomerization of 1,3-C4H6 to 1,2-butadiene (1,2-C4H6) and to include subsequent decomposition of the 1,2-C4H6 to C3H3 and CH3. The present data and other shock tube data reported over a wide pressure range were qualitatively modeled with a 89 reaction mechanism, which included the isomerizations of 1,3-C4H6 to 1,2-C4H6 and 2-butyne (2-C4H6).
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Ninomiya, Natsuhiko,Masaoka, Hiromitsu,Nakamura, Takuji,Kawano, Hiroyuki
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p. 137 - 151
(2007/10/03)
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- Reactions of laser-ablated Be and Mg atoms with C2H2: Infrared spectra and density functional calculations of novel metal-acetylene species
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Reactions of laser-ablated Be and Mg atoms with C2H2, 13C2H2, and C2D2 upon condensation in excess argon at 10 K give new infrared absorptions that are assigned to the insertion and decomposition products HBeCCH, BeCCH, and MgCCH with the help of density functional theory isotopic frequency calculations. The 2019-cm-1 C≡C stretching fundamental for BeCCH is between values for BCCH and AlCCH, which are all slightly blue shifted from acetylene itself.
- Thompson, Craig A.,Andrews, Lester
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p. 10242 - 10249
(2007/10/03)
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- Efficient chemical vapour deposition of hydrocarbon polymeric films by UV laser induced photolysis of 3-butyn-2-one
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ArF and XeCl laser induced photolysis of 3-butyn-2-one in the gas phase affords ethane, buta-1,3-diyne, ethyne and methane as minor gaseous products and a thin film of a carbon-rich organic polymer as a major product. The reaction is suitable for low-temperature chemical vapour deposition of adhesive hydrocarbon films.
- Pola, Josef,Ouchi, Akihiko,Saito, Kimitsugu,Ishikawa, Keiichiro,Koga, Yoshinori
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p. 279 - 283
(2007/10/03)
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- The pyrolysis of 3-picoline: Ab initio quantum chemical and experimental (shock tube) kinetic studies
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The pyrolysis of 3-picoline dilute in argon was investigated using a single-pulse shock tube over the temperature range of 1400-1650 K and total pressures of 12-13 atm. The principal products observed were HCN, acetylene, benzene, cyanoacetylene, methane, and pyridine. Assuming that 3-picoline decomposes according to first-order kinetics, the rate constant for its overall disappearance was determined to be kdis = 1016.9(±0.8) exp[-99 (±6) kcal mol-1/RT] s-1. The principal initial decomposition routes were found to be via the formation of the 3-picolyl and m-pyridyl radicals whose subsequent ring-opening led to the observed products. A 68-step kinetic model was developed that successfully fits the experimental data. The dominant reactions, i.e., the formation of picolyl and pyridlyl radicals and their subsequent chain-opening reactions, were studied using ab initio quantum chemical techniques. The ab initio data were also incorporated into the kinetic model in the form of energies and A-factors for reactions for which no kinetic or thermochemical data were previously available. Optimization of the kinetic model yields a value of 64 ± (3) kcal mol-1 for the heat of formation of 3-picolyl, a value lower than that for 2-picolyl, suggesting that the decomposition of 3-picoline more closely resembles that of toluene, rather than its isomer 2-picoline.
- Jones, Jeffrey,Bacskay, George B.,Mackie, John C.
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p. 239 - 248
(2007/10/03)
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- Thermal isomerization of azulene. Single-pulse shock tube investigation
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The thermal isomerization of azulene was studied behind reflected shocks in a pressurized driver single-pulse shock tube. The temperature range covered was 1050-1400 K at overall densities of ~2.5 × 10-5 mol/cm3. The main reaction of azulene under these conditions is a unimolecular isomerization to naphthalene, but it also isomerizes, although at a much lower rate, to another isomer. The suggested tetracyclic triene intermediate structure for the uzulene-naphthalene isomerization can lead also to transition states that can describe isomerizations to 1-methylene-1H-indene and 1,2,3-metheno-1H-indene,2,3-dihydro. Small quantities of C2H2, C4H2, C6H6, and C6H5-C≡CH were also found in the post-shock samples, particularly at high temperatures. The Arrhenius parameters of the two high pressure limit rate constants for the isomerization processes are: azulene ??? naphthalene, k1 = 1012.93 exp(-62.8 × 103/RT) s-1 azulene → second isomer, k2 = 1012.42 exp(-69.5 × 103/RT) s-1 A discussion of the mechanism for these isomerization processes is presented. * Author to whom correspondence should be addressed.
- Laskin, Alexander,Lifshitz, Assa
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p. 257 - 261
(2007/10/03)
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- Absolute IR Band Intensities of Diacetylene in the 250-4300 cm-1 Region: Implications for Titan's Atmosphere
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The infrared spectrum of C4H2, butadyine (also called diacetylene), has been experimentally investigated in the region from 250 to 4300 cm-1 using a Fourier transform spectrometer.A total of 12 bands have been analyzed.For each band, the characteristic wavenumber has been deduced and the values of the absolute band intensities have been systematically determined together with their associated uncertainties.The results provide important data for planetary studies.In particular, a better estimate of the mean statospheric abundance of butadiyne in Titan's atmosphere is obtained: its value is about 50percent higher than previously reported.
- Khlifi, M.,Paillous, P.,Delpech. C.,Nishio, M.,Bruston, P.,Raulin, F.
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p. 116 - 122
(2007/10/02)
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- 1,4-C,H Insertion of Vinyl Vinylidene to Intermediate Cyclobutadiene does not occur during Flash Vacuum Pyrolysis of 1-Buten-3-yne
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1-Buten-3-yne (1) and 1-buten-3-yne (1a) have been treated between 800 and 1000 deg C under flash vacuum pyrolysis as well as under gas phase pyrolysis in nitrogen and the effluents thoroughly analyzed by GC, GC/MS, GC/FTIR, 1H- and 2H-NMR spectrosco
- Hofmann, Joerg,Zimmermann, Gerhard,Findeisen, Matthias
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p. 3831 - 3832
(2007/10/02)
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- Thermal Isomerization and Decomposition of 1,2-Butadiene in Shock Waves
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1,2-Butadiene diluted with Ar was heated behind reflected shock waves over the temperature and the total density ranges of 1100 - 1600 K and 1.36*10-5 - 1.75*10-5 mol/cm3.The major products were 1,3-butadiene, 1-butyne, 2-butyne, vinylacetylene, diacetylene, allene, propyne, C2H6, C2H4, C2H2, CH4, and benzene, which were analyzed by gas-chromatography.The UV kinetic absorption spectroscopy at 230 nm showed that 1,2-butadiene rapidly isomerizes to 1,3-butadiene from the initial stage of the reaction above 1200 K.In order to interpret the formation of 1,3-butadiene, 1-butyne, and 2-butyne, it was necessary to include the parallel isomerizations of 1,2-butadiene to these isomers.The present data were successfully modeled with a 82 reaction mechanism.From the modeling, rate constant expressions were derived for the isomerization 1,2-butadiene = 1,3-butadiene to be k3 = 2.5*1013 exp(-63 kcal/RT) s-1 and for the decomposition 1,2-butadiene = C3H3 + CH3 to be k6 = 2.0*1015 exp(-75 kcal/RT) s-1, where the activation energies, 63 kcal/mol and 75 kcal/mol, were assumed.These rate constants are only applicable under the present experimental conditions, 1100 - 1600 K and 1.23 - 2.30 atm.
- Hidaka, Yoshiaki,Higashihara, Tetsuo,Ninomiya, Natsuhiko,Oki, Takashi,Kawano, Hiroyuki
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p. 331 - 342
(2007/10/02)
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- Photochemistry of Acetylene at 193.3 nm
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The quantum yield (QY) of diacetylene in the 193.3 nm photolysis of acetylene has been measured as a function of pressure, decomposition, and added gases.The QY of diacetylene is near unity (0.9 +/-0.1) when the decomposition is 1percent or less.The QY of C2H2 + hν -> C2H + H is 0.3 +/- 0.1, which is determined by the C2HD yield from the photolysis of C2H2 + C2D6 (or D2) mixtures.The yields is in good agreement with the QY of H atoms photodissociated from C2H2; C2H reacts with C2H2 to produce an equivalent amount of diacetylene.The remaining 60-70percent diacetylene arises from the metastable acetylen (C2H2**) reacting with ground-state acetylene at 193.3 nm and above 0.1 Torr of acetylene.The quenching of diacetylene formed via C2H2** by various foreign gases at various wavelengths is compared.The quenching order at 193.3 nm is N2 D2 H2 C2D6 n-C4H10.It is postulated that an adduct from C2H2** + C2H2 is initially formed before it dissociates into C2H4 + H2 or C2H + C2H3.Yields of C4H2, C2HD, and C2H2 were measured by FT-IR calibrated with pure samples.The C4H2 yield at 193 nm does not change with addition of N2 up to 600 Torr.The absorption cross section of C2H2 has been measured in the 190 - 230-nm region.The production of C4H2 was examined at wavelength below and above the dissociation threshold.The metastable acetylene reactions may be important in haze formation in Titan's atmosphere.
- Seki, Kanekazu,Okabe, Hideo
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p. 5284 - 5290
(2007/10/02)
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- Laboratory Studies of Low-Temperature Reactions of C2H with C2H2 and Implications for Atmospheric Models of Titan
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Rate coefficients for the reaction C2H + C2H2 --> C4H2 + H are measured over the temperature range 170-350 K.The reactions are carried out in a temperature variable flow cell.C2H radicals are produced by pulsed laser photolysis of C2H2, and a tunable infrared color-center laser is used to probe the transient removal of C2H in absorption to derive the rate coefficients.The results show that the rate coefficient is independent of temperature over the range 170-350 K and equal to (1.1 +/- 0.2) * 10-10 exp cm3 molecule-1 s-1.The reaction studied is of central importance for models of the photochemistry of the atmospheres of the outer planets, in particular for the satellite Titan, and the implications of the present results for these models are discussed.
- Pedersen, Jens Olaf P.,Opansky, Brian J.,Leone, Stephen R.
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p. 6822 - 6829
(2007/10/02)
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- Kinetics of the Reactions of C2H with C2H2, H2, and D2
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Kinetics of the reactions C2H + C2H2 --> C4H2 + H (1), C2H + H2 --> C2H2 + H (2), and C2H + D2 --> C2HD + D (3) have been studied at T = 293 K with two time-resolved diagnostics, laser-induced fluorescence (LIF) detection of H (or D) atoms at the Lyman-α wavelength and mass spectrometric detection of C4H2.The C2H radical was prepared by the ArF (193 nm) laser photolysis of C2H2.Measurements of the yield of H (or D) atom indicated that the C2H radicals produced by the photolysis were converted effectively to H (or D) atoms; i.e. formation of the stable intermediatessuch as C4H3, C2H3, or C2HD2 was negligible under the present experimental conditions (p = 30 Torr).Rate constants of k1 = (1.6 +/- 0.1) * 10-10, k2 = (7.1 +/- 1.1) * 10-13, and k3 = (2.0 +/- 0.3) * 10-13 cm3 molecule-1 s-1 were derived from the pseudo-first-order rise rates of the H (or D) atom.Rate constant of k1 = (1.4 +/- 0.3) * 10-10 cm3 molecule-1 s-1 was also obtained at p = 5 Torr by measuring the appearance rate of C4H2.The ratios of the rate constants k2/k1 = (3.4 +/- 0.2) * 10-3 and k3/k1 = (1.4 +/- 0.5) * 10-3 were deduced by measuring the dependence of the C4H2 production on the partial pressure of added H2 or D2.Transition state theory calculations on the basis of ab initio transition-state properties demonstrated the importance of the tunnel effect for reaction 2 at room temperature.
- Koshi, Mitsuo,Nishida, Nobuhiro,Matsui, Hiroyuki
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p. 5875 - 5880
(2007/10/02)
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