- Reactions of C3H3+ with Acetylene and Diacetylene in the Gas Phase
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The reactions of linear C3H3+ with acetylene, diacetylene, and deuteriated acetylene were investigated with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer.A rate coefficient of (1.4 +/- 0.7)E-9 cm3/s was obtained for the reaction of linear C3H3+ with diacetylene while no production of larger ions was observed with acetylene.The ejection capabilities of FTICR were used to study the reactions of different C3H3+ precursors with C2H2 in order to investigate the possible production of C5H5+ from ionic sources other than C3H3+ present in the reaction medium.Linear C3H3+ isomerized to the cyclic form in the reactions with both acetylene and diacetylene.The isomerization was shown to take place via a long-lived C5H5+ complex by isotope exchange reactions between linear C3H3+ and deuteriated acetylene.Results are discussed in relation to previous work involving C3H3+ reactions and a proposed ionic route to soot formation.
- Ozturk, F.,Baykut, G.,Moini, M.,Eyler, J. R.
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- Comparison of bending, C-C stretching, and collision energy effects on the reaction of C2H2+ with D2
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We report the effects of vibrational excitation and collision energy on the cross sections and branching ratios for reaction of acetylene cations with D2, using two different guided-ion-beam instruments.Two major reaction channels are observed, both of which are nearly thermoneutral.Hydrogen atom exchange is slightly exoergic due to zero point energy, and is inhibited by both collision and vibrational energy.Formation of the two isotopic C2H3+ products is enhanced by collision energy and C-C stretching vibration, but not by bending vibration.The branching ratios at low collision energies are consistent with reaction via an intermediate complex, and Rice-Ramsberger-Kassel-Marcus (RRKM) analysis is used to extract further information.At collision energies above 1 eV, D-atom transfer by a direct mechanism is also observed as a route to C2H2D+ production.Comparison of our results using both the Stony Brook and Freiburg instruments is made with the state-selected experiments of Honma, Kato, Tanaka, and Koyano , who previously studied both the C2H2+ + D2 and C2D2+ + H2 isotopic reactants.Our results for C2H2+ + D2 are consistent with their C2D2+ + H2 data for all collision energies and with their C2H2+ + D2 data at 0.2 eV collision energy.We do not reproduce the anomalous vibrational effects they reported for 1 and 2 eV collision energies.
- Chiu, Yu-hui,Yang, Baorui,Fu, Hungshin,Anderson, Scott L.,Schweizer, Martin,Gerlich, Dieter
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- Mechanistic studies on platinum(II) catalyzed hydroarylation of alkynes
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The dicationic acetylene platinum(II) complex [Pt(PNP)(C2H 2)](BF4)2 (PNP = 2,6- bis(diphenylphosphinomethyl)pyridine) was generated in situ by ligand substitution from the ethylene complex [Pt(PNP)(C2/sub
- Hahn, Christine,Miranda, Mayra,Chittineni, Nagendra P. B.,Pinion, Trent A.,Perez, Ricardo
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- Contrasting Free Energies of Electron Transfer from - and Annulenes to Their Perdeuteriated and Per-(13)C Analogues
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A very large equilibrium isotope effect (confirmed via physical, separation oof the isotopes involved) was observed via the EPR analysis of a mixture of benzene and perdeuteriated-per-(13)C-benzene competing for a deficient number of electrons in tetrahyydrofuran (THF) in the presence of 18-crown-6 (18C6).The Keq for the reaction C6H6.-, K+(18C6) + (13)C6D6 = C6H6 + (13)C6D6.-, K+(18C6) is 0.096 +/- 0.008 at 100 deg C.An analogous competition for electrons exists between annulene and perdeuteriated-per-(13)C-annulene.In contrast to the benzene system the Keq for the reaction C8H8.-, Na+ + (13)C8D8 = C8H8 + (13)C8D8.-,Na+ in liquid ammonia is 1.20 +/- 0.04 at -100 deg C.Similar contrasting results (but smaller in magnitude) were observed for the benzene and cyclooctatetraene perdeuteriated and per -(13)C systems.The results are interpreted in terms of the divergence of the annulene system from aromatic character upon electron addition and the convergence of the annulene system toward aromatic character upon electron addition.
- Stevenson, Gerald R.,Peters, Steven J.,Reidy, Kerry A.,Reiter, Richard C.
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- MICROWAVE ROTATIONAL SPECTRUM AND PROPERTIES OF HYDROGEN-BONDED DIMER FORMED BY TRIMETHYLAMINE AND ACETYLENE
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The rotational spectra of the four isotopic species (CH3)3-14N...HCCH, (CH3)3-14N...DCCH, (CH3)3-14N...HCCD and (CH3)3-14N...DCCD of a hydrogen-bonded dimer formed between trimethylamine and acetylene have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy.The ground-state spectroscopic constants determined for these symmetric-top molecules are: For (CH3)3-14N...HCCH it has been established that the 14N-nuclear quadrupole coupling constant varies linearly with K2 according to χ(K) = χ(K = 0) + (6.6*10-3)K2 MHz.The following molecular properties have been determined for the dimer from the spectroscopic constants: r(N...C) = 3.254(4) Angstroem, θav = 15.43(9) deg and k? = 5.82(2) N m-1.
- Legon, A. C.,Rego, C. A.
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- Rotational spectroscopy of mixtures of ethyne and iodine monochloride: Isolation and characterisation of the π-type complex C2H2···ICl
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The ground-state rotational spectrum of a complex formed by ethyne and iodine monochloride was observed by using pulsed-nozzle, Fourier-transform microwave spectroscopy. A fast-mixing nozzle was utilised to avoid chemical reaction of the component gases prior to their supersonic expansion. Rotational constants A0, B0 and C0, quartic centrifugal distortion constants Δ(J), Δ(JK) and δ(J), and halogen nuclear quadrupole coupling constants χ(aa)(X) and {χ(bb)(X) χ(cc)(X)}, where X = Cl or I, were determined for the three isotopomers C2H2···I35Cl, C2H2···I37Cl and C2D2···I35Cl. Detailed interpretation of the rotational constants established that the equilibrium geometry of the complex has a planar, T- shape of C(2v) symmetry in which ethyne acts as the bar of the T. This geometry, with the zero-point distance r(*···I) = 3.115(1) A between the centre of the π-bond of ethyne and the nearest halogen atom I, establishes that the interaction in this complex is between ethyne as a π electron donor and I of ICl as the electron acceptor. The halogen nuclear quadrupole coupling constants χ(aa)(X) were interpreted on the basis of a simple model to show that, on complex formation, fractions δ1 = 0.026 and δ2 = 0.056 of an electronic charge are transferred from the ethyne π bond to I and from I to C1, respectively, leading to a net decrease of 0.030e at I. The complex is weakly bound, according to the intermolecular stretching force constant kσ = 12.2(1) Nm-1 determined for the isotopomers C2H2···I35Cl and C2H2···I37Cl from Δ(J) values. The opportunity is taken to compare the properties of C2H2···ICl established here with those similarly determined for the series C2H2···XY, where XY = Cl2, ClF, or BrCl.
- Davey,Legon
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- The phenylcyclooctatetraene anion radical and dianion: An intramolecular charge and spin distribution isotope effect
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EPR studies on the anion radicals and 13C NMR studies of the dianions of phenylcyclooctatetraene ([6]-[8]), phenylcyclooctatetraene-d7, and phenyl-d5-cyclooctatetraene show that deuteriation of the cyclooctatetraenyl moiety perturbs and phenyl group spin and charge distributions in the anion radical and dianion, respectively. However, deuteriation of the phenyl moiety does not alter these distributions in the cyclooctatetraenyl moiety. The upfield shift in the chemical shifts of the phenyl carbons in the dianion and the increased spin density in the phenyl moiety in the anion radical, resulting from deuteriation of the eight-membered ring, is explained in terms of the different degrees of twist between the COT and phenyl rings. Since there is more zero-point energy in the coplanar arrangement and the force constant for C-D or C-H stretching mode should be maximized in a coplanar arrangement, [6]-[8]*- will tend to be more twisted than will [6]-[8]-d7*-. The deuteriation studies have further shown that the nature of the spin distribution in the anion radical of [6]-[8] has long been fundamentally misunderstood.
- Stevenson, Gerald R.,Burton, Richard D.,Reiter, Richard C.
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- Deuterium Nuclear Magnetic Resonance spectroscopy. 1 - Larmor Frequency Ratio, Referencing and Chemical Shift
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Precise values for the ratio of the Larmor frequencies, w1H/w2H, were measured at constant field for various organic compounds.The values of the Larmor frequency ratio depend on carbon-hydrogen bond hybridization.The best ratio for the ghost referencing of 2H NMR spectra was then determined (6.514399862).This value enables an accurate ghost reference for any 2H NMR spectrum to be derived from the observed 1H NMR frequency of the normal internal reference.Deuterium and proton chemical shifts measured from internal, partially deuteriated TMS under the same conditions are shown to be the same.
- Al-Rawi, Jasim M. A.,Behnam, George Q.,Taha, Nihad I.
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- INTERNAL ROTATION AND FRAMEWORK RELAXATION IN ETHENE THIOL
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New and existing data on the ground and excited CS torsional states of the stable rotamers of ethene thiol have been analysed to give a potential function for internal rotation around the CS bond.The barrier between the syn and anti rotamers is found to be 800 cm-1 and that at the planar anti conformation itself to be 12 cm-1.The syn conformation is 50 cm-1 more stable than the 'quasi-planar' anti conformation.Satisfactory reproduction of the observed trends in rotational constants with torsional excitation has been achieved by introducing extensive relaxation of the CCS angle and the CS bond length during internal rotation.The CCS angle reduces by up to 5 deg whilst the CS bond length increases by up to 0.02 Angstroem during rotation from the syn to anti conformation.The use of ab initio M.O. calculations to provide an indication of the most significant aspects of structure relaxation is described.
- Almond,V.,Permanand, R. R.,Macdonald, J. N.
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- Thermal rearrangement of 2,5-bis(dicyanomethylene)bicyclo[4.2.0]oct-7-ene and 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene. Unexpected formation of 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-1(5)-ene and -octa-3,7-diene, new electron acceptors
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Upon heating at 200 °C in o-dichlorobenzene, 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-3,7-diene gave rise to 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-3,7-diene by a rearrangement as a sole isolable product in modest yield, and no trace of 5,8-bis(dicyanomethylene)cycloocta-1,3,6-triene, the expected product, was detected. On the other hand, 2,5-bis(dicyanomethylene)bicyclo[4.2.0]octa-7-ene underwent a thermal reaction at lower temperature (110 °C in toluene) to give 5,8-bis(dicyanomethylene)-1,3-cyclooctadiene, the normal ring-opened product, and 2,6-bis(dicyanomethylene)bicyclo[3.3.0]octa-1(5)-ene, a rearranged product, in about 1:1 ratio. The rearranged product has a planar 1,1,6,6-tetracyanohexatriene structure (X-ray analysis), and shows a considerably lower electron affinity than that of tetracyano-ethylene and 7,7,8,8-tetracyano-p-quinodimethane. The electron acceptor also formed a crystalline 1:1 charge transfer complex with tetrathiafulvalene, of which electronic conductivity was near insulating (1.1 × 10-7 S cm-1). We have proposed a possible mechanism for the rearangements involving the zwitterionic intermediates.
- Kawase, Takeshi,Okada, Tomoaki,Enomoto, Tetsuya,Kikuchi, Takayuki,Miyake, Yoji,Oda, Masaji
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- Bioinspired Nucleophilic Attack on a Tungsten-Bound Acetylene: Formation of Cationic Carbyne and Alkenyl Complexes
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Inspired by the proposed inner-sphere mechanism of the tungstoenzyme acetylene hydratase, we have designed tungsten acetylene complexes and investigated their reactivity. Here, we report the first intermolecular nucleophilic attack on a tungsten-bound acetylene (C2H2) in bioinspired complexes employing 6-methylpyridine-2-thiolate ligands. By using PMe3 as a nucleophile, we isolated cationic carbyne and alkenyl complexes.
- Ehweiner, Madeleine A.,Peschel, Lydia M.,Stix, Niklas,Córovi?, Miljan Z.,Belaj, Ferdinand,M?sch-Zanetti, Nadia C.
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- The Steric Course of the Reaction of Ethylene Oxide with Hydrogen Halides in the Gas Phase
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The steric course of the gas-phase reaction of trans-ethylene oxide with HF, HCl, and HBr was investigated in order to test experimentally a mechanistic proposal based on ab initio calculations involving a concerted syn-opening mechanism.In contrast with this proposal the reactions with HCl and HBr take place entirely with anti-opening of the ring to give erythro-2-chloro- and 2-bromoethanol.The reaction of ethylene oxide with gaseous HF yields only 5percent 2-fluoroethanol, 37percent dioxan, oligomers and polymers being the main products.An inproved method for the conversion of cis- and trans-ethylene into the corresponding epoxides is described.
- Bellucci, Giuseppe,Berti, Giancarlo,Bianchini, Roberto,Ingrosso, Giovanni,Moroni, Antonio
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- Isolated Fe(III)-O Sites Catalyze the Hydrogenation of Acetylene in Ethylene Flows under Front-End Industrial Conditions
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The search for simple, earth-abundant, cheap, and nontoxic metal catalysts able to perform industrial hydrogenations is a topic of interest, transversal to many catalytic processes. Here, we show that isolated FeIII-O sites on solids are able to dissociate and chemoselectively transfer H2 to acetylene in an industrial process. For that, a novel, robust, and highly crystalline metal-organic framework (MOF), embedding FeIII-OH2 single sites within its pores, was prepared in multigram scale and used as an efficient catalyst for the hydrogenation of 1% acetylene in ethylene streams under front-end conditions. Cutting-edge X-ray crystallography allowed the resolution of the crystal structure and snapshotted the single-atom nature of the catalytic FeIII-O site. Translation of the active site concept to even more robust and inexpensive titania and zirconia supports enabled the industrially relevant hydrogenation of acetylene with similar activity to the Pd-catalyzed process.
- Tejeda-Serrano, María,Mon, Marta,Ross, Bethany,Gonell, Francisco,Ferrando-Soria, Jesús,Corma, Avelino,Leyva-Pérez, Antonio,Armentano, Donatella,Pardo, Emilio
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- Formation of D and H Atoms in the Pyrolysis of Benzene-d6 and Chlorobenzene behind Shock Waves
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Dilute mixtures (3-20 ppm) of C6D6 (benzene-d6) were pyrolyzed behind reflected shock waves at temperatures of 1630-1940 K and total pressures of 2-3 atm.Progress of the reaction was followed by analysis for D atoms using resonance absorption spectroscopy.Appearance of D atoms was a first-order process with respect to benzene concentration, and with respect to time during the first part of each experiment.An Arrhenius equation for the formation of D atoms, based on 34 experiments, is kD = 9.7E12 exp(-87100 cal/RT) s-1 with an estimated uncertainty of a factor of 1.5.From measurements of H atoms during pyrolysis of chlorobenzene under similar conditions at 1570-1790 K, the first-order rate constant for the dissociation of chlorobenzene to chlorine atoms and phenyl radicals was found to be k6 = 1.2E14 exp(-90000 cal/RT) s-1, and that for the dissotiation of phenyl radicals to H atoms and other products k3a = 1.2E15 exp(-82000 cal/RT) s-1.With this information, the rate constant for dissociation of benzene-d6 to phenyl-d5 and D atoms was found to be k1D = 4.6E13 exp(-95000 cal/RT) s-1.The rate constant for the exchange reaction H + C6D6 -> C6D5H + D was found to be k4a = 3.2E13 exp(-4200 cal/RT) mol-1 cm3 s-1 over the range 300-1400 K by combining our results with others at lower temperatures.A very simple kinetic model based on a reaction chain with H as carrier can relate our data to other shock-tube work at higher benzene concentrations.
- Rao, V. Subba,Skinner, Gordon B.
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- The Anion Radical of Bicyclononatriene
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The low-temperature potassium metal reduction of bicyclonona-2,4,6-triene (BCN) in DME leads to the formation of the previously observed open form of the homocyclooctatetraene anion radical (HCOT anion radical).Careful inspection of the EPR spectra recorded from these solutions, and some of those previously published, shows the presence of another species.This second species is best interpreted using a set of methylene proton coupling constants very similar to those of HCOT anion radical (all within 10percent) but much smaller endo and exo bridgehead coupling constants.Perdeuteriation of of the sp2 carbons supports this interpretation.The only reasonable interpretation of the hyperfine pattern observed for the second anion radical is in terms of the closed (bicyclic) form.The closed anion radical (BCN anion radical) is favored under conditions involving more ion association and more complete reduction.
- Stevenson, Gerald R.,Burton, Richard D.,Reiter, Richard C.
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- Site and isotope effects on the molecular hydrogen elimination from ethylene at 157 nm excitation
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Site and isotope effects on the molecular hydrogen elimination from ethylene have been studied from the photodissociation of ethylene at 157 nm excitation. Experimental results show that there are three different types of molecular elimination processes: 1,1 elimination, 1,2-cis elimination, and 1,2-trans elimination. These elimination processes show significantly different translational energy distributions. Isotope effect on the dynamics of these molecular hydrogen elimination processes has been also investigated carefully.
- Lin, Jim J.,Hwang, Dennis W.,Lee, Yuan T.,Yang, Xueming
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- Deuterium Isotope Effects on Nuclear Shielding. Directional Effects and Nonadditivity in Acyl Derivatives
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Deuterium isotope effects on the 19F and 13C nuclear shieldings have been investigated in acyl derivatives.A nonadditivity of the 3ΔF(D) of acetyl fluoride has been experimentally established and related primarily to nonuniform rotamer distributions of the mono- and dideuteriated isotopomers.The 3ΔF(D)'s show furthermore a distinct orientational dependence.The isotope effects for the configurations where the nuclei in question are in a trans position are positive and those in which they are gauche are negative.The 2ΔCO(D)'s are negative and additive in all the investigated cases.The observed isotope effects are discussed in general in terms of substituent and vibrational effects.
- Hansen, Poul Erik,Nicolaisen, Flemming M.,Schaumburg, Kjeld
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- Collisional Quenching of Excited Vinylidene (3B2) Radicals
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Rate constants for the removal of excited-state vinylidene D2CC (3B2) in the presence of He, Ar, N2, H2, CO, and CH4 are reported at room temperature.The excited vinylidene radicals are generated via vacuum-ultraviolet photolysis of mixtures of C2D3Cl in the quencher gases through the reeaction sequence C2D3Cl -> C2D3Cl*; C2D3Cl* -> D2CC (3B2) + DCl.Excited triplet vinylidene radicals are then collisionally quenched to the singlet ground state with undergoes rapid isomerization to acetylene.Rate constants for removal of D2CC (3B2) by quenchers are determined by observation of the time-resolved absorption of either D2CC (3B2) at 137 nm or product C2D2 at 151 nm.The observed quenching rate constants for the deuterated species are kHe = (1.9 +/- 0.3) * 10-15, kAr = (6.64 +/- 0.3) * 10-15, kN2 = (8.5 +/- 0.2) * 10-15, kH2 = (33.8 +/- 6.1) * 10-15, kCO = (28.0 +/- 8.0) * 10-15, and kCH4 = (28.0 +/- 8.0) * 10-15 cm3 molecule-1 s-1.No evidence for chemical reaction could be observed.The derived quenching cross sections are correlated with the potential well depth model.This correlation is valuable in predicting nonreactive collisional cross sections for additional gases.
- Fahr, Askar,Laufer, Allan H.
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- Structure of the Bromovinyl Radical: a Matrix Isolation Study
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The bromovinyl radical has been prepared by the reaction of bromine atoms with acetylene in an argon matrix at 17 K and its i.r. spectrum has been studied.The spectrum of C2HDBr. shows the presence of two isomers, indicating that the radical has an unsymmetric structure.
- Engdahl, Anders,Nelander, Bengt
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- The kinetics of the H2 (D2) loss from C2H4+ (C2D4+) ions
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The unimolecular H2/D2 loss from C2H4+/C2D4+ ions has been investigated in a threshold photoelectron photoion coincidence spectrometer with electron time of flight discrimination. The experiment shows that the reaction takes place on the microsecond timescale, i.e. is metastable right at the threshold. The experimental breakdown curve for d4-ethene is shifted by 103 meV to a higher excitation energy compared to h4-ethene. The entire breakdown curves were simulated based on model k(E) curves. Best agreement between experiment and simulation was observed for threshold values of k(E0) = 7.0 x 105 s-1 for h4-ethene and k(E0) = 2.5 x 104 s-1 for d4- ethene.
- Malow, Marcus,Guethe, Felix,Weitzel, Karl-Michael
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- deuterium generation ethylene preparation method
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The invention discloses a preparation method of deuteroethylene. According to the preparation method, calcium carbide is reacted with D2O to generate deuteroacetylene; a deuteration reaction is performed on the prepared deuteroacetylene and deuterium gas in the presence of a composite catalyst Cu-Ni/SiO2 to obtain the deuteroethylene; the volume ratio of the deuteroacetylene to the deuterium gas is 1: (10-60). The preparation method of the deuteroethylene is applicable to industrial production and has been verified and utilized in an industrial pilot plant already; experimental results prove that the preparation method has the advantages of simple reaction steps, mild reaction conditions, high deuteroethylene yield, recyclability of superfluous deuterium gas in the reaction as the raw material, and great reduction of the production cost.
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Paragraph 0037-0038
(2018/02/04)
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- Deuteration and dimerization of acetylene with a nieuwland catalyst in deuterium oxide
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Efficient deuteration and dimerization of acetylene have been readily attained in deuterium oxide with a Nieuwland catalyst which is practically used for dimerization of acetylene. Copyright
- Tachiyama, Takashi,Yoshida, Makoto,Aoyagi, Tatsuhiro,Fukuzumi, Shunichi
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- Deuterium Isotope Effect in Vinyl Radical Combination/Disproportionation Reactions
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The deuterium isotope effect for the vinyl radical combination and disproportionation reactions have been investigated.Protonated or deuterated vinyl and methyl radicals are produced from the 193 nm photolysis of protonated or perdeuterated methyl vinyl ketone.On the basis of product yield measurements, no isotope effect for the combination reactions of either vinyl-vinyl or vinyl-methyl has been observed.From the relative yields of ethylene, an isotope effect of kH/kD = 1.20 is determined for the vinyl-vinyl disproportionation reaction.
- Fahr, Askar,Laufer, Allan H.
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p. 262 - 264
(2007/10/02)
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- Ultraviolet and Polarized Infrared Spectroscopy of Matrix-Isolated Cyclobutadiene and Its Isotopomers
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The UV and polarized IR spectra of argon matrix isolated cyclobutadiene and its 1-d-, 1,2-d2-, 1,4-d2-, 1-13C-, 1,2-13C2-, and 1,4-13C2- labeled derivatives are reported.Above 250 nm, the UV spectrum contains no peaks with an extinction coefficient larger than 10 L M-1 cm-1, but a weak absorption tail extends throughout the UV region.The absorption rises abruptly below 250 nm.The IR peak positions mostly agree with previous reports where these are available.Photoalignment studies support the symmetry assignment of fundamental vibrations and prove that the two Kekule forms interconvert rapidly even at 10 K.The spectral and photochemical effe ts of the presence of an adjacent CO2 molecule in the cyclobutadiene matrix site are elucidated.Its presence causes a substantial retardation of the photofragmentation of cyclobutadiene into two acetylenes.This is attributed to accelerated vibrational energy loss from the cyclobutadiene absorber.
- Arnold, Bradley R.,Michl, Josef
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p. 13348 - 13354
(2007/10/02)
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- Matrix Isolation Study of the Dissociation and Isomerization Pathways of Benzene following Corona Discharge Excitation
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Reactions of C6H6 and C6D6 after exposure to a corona-excited discharge have been studied by the trapping of products into an argon matrix at 14 K.Infrared spectroscopy was employed to identify product species; most were known species and identified by comparison to literature spectra.Tentative assignments for several previously unreported deuterated products are made.The product distribution included species from both rearrangement and dissociation processes.In general, the product distribution differed from previous UV irradiation studies; a mechanism for product formation is proposed.The effectiveness of the corona excitation discharge as a simple source for the generation of transient organic species for matrix spectroscopic study was confirmed.
- Bai, Hebi,Ault, Bruce S.
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p. 9169 - 9172
(2007/10/02)
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- Gas-phase reactions of tantalum carbide cluster ions with deuterium and small hydrocarbons
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The gas-phase ion/molecule reactions of tantalum carbide cluster ions (TaCy+, y = 0-14) with D2, CH4, C2H4, and C2H6 have been investigated by Fourier transform mass spectrometry. Product branching ratios and reaction rate constants are reported. The addition of tantalum dramatically alters the reactivity relative to that of the corresponding carbon clusters (Cy+), leading to the conclusion that the TaCy+ reactions are initiated on the metal. In addition, the extensive dehydrogenation and secondary reactivity that characterize the reactions of Ta+ with hydrocarbons are observed for TaCy+. Experiments with isotopically labeled precursors were performed, as well as low-energy collision-induced dissociation studies of major reaction products. The implications of these studies with respect to TaCy+ structures and reaction mechanisms are discussed. Total scrambling of the labeled carbon occurred during the TaCy+ reactions with 13CH4. This indicates that the mechanism involves incorporation of the methane carbon into the Cy ligand(s) prior to elimination of a neutral and suggests the possibility of cyclic TaCy+ structures. Evidence is also presented for two structural isomers of TaC7+, TaC8+, and TaC9+.
- Cassady, Carolyn J.,McElvany, Stephen W.
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p. 4788 - 4797
(2007/10/02)
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- MICROWAVE SPECTRA AND STRUCTURE OF DICHLOROETHENES
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The complete rs structures for both 1,1- and cis-1,2-dichloroethenes have been derived from isotopic measurements for each isotopic position.The accuracy of the structural parameters obtained is discussed on the basis of isotope effect on bond lengths caused by zero-point vibrations, and it is suggested that more than 0.01 Angstroem of additional uncertainty originating from the isotope effect must be considered for the bond lengths determined by means of the Kraitchman method.The quadrupole coupling constants are re-evaluated by use of the newly determined structures.
- Takeo, Harutoshi,Sugie, Masaaki,Matsumura, Chi
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p. 205 - 214
(2007/10/02)
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- COMPARATIVE STUDY OF cw CO2 LASER INDUCED AND SF6 SENSITIZED DECOMPOSITION OF METHYL IODIDES CH3I AND CD3I
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The decomposition of methyl iodide-d3 initiated by the irradiation of a cw CO2 laser in the presence of SF6 proceeds under comparable conditions faster, particularly in the shorter wavelength region of the CO2 laser spectrum, than the decomposition of methyl iodide.The differences can be explained by the different distribution of energy levels of both reactants.Observable differences are also in the composition of the reaction products.All these facts indicate the participation of at least two reaction mechanisms, a radical one and a molecular one, which canprobably proceed via the collision of two vibrationally excited molecules of CX3I.
- Rejnek, Jaroslav,Engst, Pavel,Jakoubkova, Marie,Horak, Milan
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p. 215 - 222
(2007/10/02)
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- The Reaction of Vinyl Ions with Methane
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The reaction of C2H3+ with CH4 have been studied in an ion beam/scattering gas apparatus at collision energies in the range of 0.5-3.2 eV and at CH4 pressures in the range of 0.5-10 mtorr.Persistent collision complexes, C3H7+, were not observed even at the highest pressures employed, indicating that the collision-complex lifetime is less than the transit time of the apparatus (20 μs) under all conditions.However, the excellent agreement of the isotopic distributions of allyl ion, propargyl ion, vinyl ion (back-reaction), and a fraction of the methyl ion in the C2D3+/CH4 and C2H3+/CD4 systems strongly suggests that a significant part of the reaction proceeds via a long-lived C3H7+* complex.A very significant part of the reaction that produces CH5+, CH3+, and C3H6+ occurs via direct processes.
- Senzer, S. N.,Lim, K. P.,Lampe, F. W.
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p. 5314 - 5319
(2007/10/02)
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- CW CO2 LASER-INDUCED AND SF6-SENSITIZED DECOMPOSITION OF METHYL IODIDE-d3
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The decomposition of CD3I initiated by the irradiation of a cw CO2 laser was studied in the presence of the SF6 sensitizer.The first reaction step of the decomposition procedures CD3 radical that yields either methane-d4 (the abstraction reaction of "hot" radicals), or ethane-d6 (the recombination reaction of "cold" radicals).The effect of the total pressure and the decomposition of the reaction mixture, that of the laser excitation line and output and that of the irradiation time upon the decomposition rate and the product distribution was examined.
- Rejnek, Jaroslav,Jakoubkova, Marie,Engst, Pavel,Horak, Milan
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p. 3261 - 3269
(2007/10/02)
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- CO2 LASER-INDUCED DECOMPOSITION OF METHYL IODIDE SENSITIZED BY SULFUR HEXAFLUORIDE
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Gaseous mixtures of methyl iodide and sulfur hexafluoride yield upon irradition by a continuous-wave CO2 laser iodine, methane, ethane, ethylene and acetylene - the products of methyl iodide decomposition.The decomposition rate and the mutual ratio of the products is dependent on the delivered irradiatiion energy, the methyl iodide/sulfur hexafluoride ratio and the energy of the exciting photon.Methyl iodide-d3 in the mixture with SF6 behaves similarly as methyl iodide yielding perdeuterated methane, ethane, ethylene, acetylene and iodine.
- Dathe, Klaus,Engst, Pavel,Pola, Josef,Horak, Milan
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p. 1910 - 1919
(2007/10/02)
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- Synthesis and Thermal Decomposition of cis-3,4,5,6-Tetrahydropyridazine-3,4-d2. Relative Rates of Rotation, Cleavage, and Closure for Tetramethylene
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The stereospecific syntheses of cis-3,4,5,6-tetrahydropyridazine-3,4-d2 (6) and cis- and trans-cyclobutane-1,2-d2 are reported.The thermal decomposition of cis-3,4,5,6-tetrahydopyridazine (6) (gas phase, 439 deg C) affords 67.1 +/- 0.9percent cis-ethylene-1,2-d2, 16.1 +/- 0.8percent trans-ethylene-1,2-d2, 9.4 +/- 0.4percent cis-cyclobutane-1,2-d2, and 7.4 +/- 0.4percent trans-cyclobutane-1,2-d2.The relative rates of rotation, cleavage, and closure for this 1,2-diazene generated tetramethylene-d2 are k(cleavage)/k(closure) = 2.2 +/- 0.2 and k(rotation)/k(closure) = 12 +/- 3.An extra stereospecific cleavage component (46percent) superimposed on the 1,4-biradical pathway (54percent) from the parent tetrahydropyridazine was found, similar to that observed in the 3,4-dimethyl-3,4,5,6-tetrahydropyridazine thermal reactions.Finally, the experimental data fot the parent 1,4 biradical, tetramethylene, are compared to calculated values in the literature.
- Dervan, Peter B.,Santilli, Donald S.
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p. 3863 - 3870
(2007/10/02)
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