- Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes
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The 193 and 157 nm photodissociations of three isomers of dichloroethylene (DCE) and trichloroethylene (TCE) were investigated using a technique of photofragmentation translational spectroscopy. The photofragmentation mechanisms were constructed by analyzing the time-of-flight spectra of C2H+2, Cl+, HCl+, C2HCl+, and C2Cl+2 produced by electron impact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C-Cl bond rupture were important for all the compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C-Cl bond rupture was important even at 193 nm. In the 157 nm photodissociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C-Cl bond rupture occurred for trans-DCE. This result suggests that the 157 nm photodissociation of trans-DCE proceeds via the direct photodissociation following the photoexcitation to the repulsive 1nσ* state. A minor C-H bond rupture was also found in the 157 nm photodissociations of cis-DCE and TCE. On the basis of the present mechanisms, the translational energy distributions and the branching ratios were estimated for all the possible processes.
- Sato, Kei,Tsunashima, Shigeru,Takayanagi, Toshiyuki,Fujisawa, Ginji,Yokoyama, Atsushi
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- Photofragmentation of mono- and dichloroethylenes: Translational energy measurements of recoiling Cl and HCl fragments
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Translational energy (Et) spectra of Cl and HCl fragments from vinylchloride, trans- dichloroethylene, cis-dichloroethylene, and 1,1'-dichloroethylene have been measured for the ?*t distribution and angular dependence of the Cl fragment indicate that the two-center dissociation occurs in a time faster than a rotation period and the recoiling organic radical (the counter fragment) is highly vibrationally excited.In dichloroethylenes, the presence of a second channel producing Cl atoms has been confirmed and attributed to the dissociation from the lower (n,?*) state through a (?,?*) state.The Et distribution of HCl fragments is nonstatistical and found to converge to null population at an energy less than half of the total available energy.This convergence point coincides with the value of the local available energy for the elimination reaction (activation energy -ΔHreaction0).The yield of HCl molecules relative to Cl atoms is estimated to be ca. 1.1 for vinylchloride.High efficiency of the HCl elimination is attributed to a rapid internal conversion from the (?,?*) state to the lowest (?,?*) state from which the pathway to the transition state for HCl elimination is opened in ground electronic manifolds.
- Umemoto, Masayuki,Seki, Kanekazu,Shinohara, Hisanori,Nagashima, Umpei,Nishi, Nobuyuki,et al.
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- Synthesis of (chlorovinyl)cobaloxime complexes, model complexes of proposed intermediates in the B12-catalyzed dehalogenation of chlorinated ethylenes
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(Chlorovinyl)cobaloxime complexes, (dmgH)2(py)CoR (R = cis-dichlorovinyl, trans-2-chlorovinyl or 1-chlorovinyl, dmgH = dimethylglyoximate) were synthesized from the reaction of chlorinated ethylenes with in situ generated (dmgH)2Co(I) in the presence of pyridine.
- Rich, Autumn E.,DeGreeff, Angela D.,McNeill, Kristopher
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- Laser photolysis of trans-dichloroethylene at 193 nm: Quantum yields of photoproducts
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The photodissociation of trans-dichloroethylene (trans-DCE) was studied using an ArF excimer laser at 193 nm. Acetylene, chloroacetylene and hydrogen chloride are observed as products, but the chlorine molecule is not observed. The yields are determined to be 0.47 ± 0.10 and 0.35 ± 0.05 for acetylene and chloroacetylene, respectively. On the basis of the reaction mechanism, the sum of the quantum yields of hydrogen chloride molecules (Φ = 0.35) and chlorine atoms (Φ = 0.94) dissociated from trans-DCE is estimated to be greater than unity. These results indicate that two chlorine atoms are successively dissociated from the parent molecule by the photolysis at 193 nm.
- Seki, Kanekazu,Kobayashi, Takanori,Ebata, Kazukiyo
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- The C-Cl bond fissions from the photolysis of CHClCCl2 at 193 nm
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The photolysis of CHClCCl2 at 193 nm was investigated by translational spectroscopy. Two distinct product translational distributions were derived for the C-Cl bond fissions. The internally excited C2HCl2 fragment from the main dissociation channel is shown to decompose totally to produce the Cl+C2HCl products.
- Lee, Yu-Jinn,Lee, Ya-Rong,Chou, Chih-Chiang,Lin, Shen-Maw
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- Reductive transformation of trichloroethene by cobalamin: Reactivities of the intermediates acetylene, chloroacetylene, and the DCE isomers
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The transformations of acetylene, chloroacetylene, 1,1-dichloroethene (DCE), and cis- and trans-DCE mediated by cobalamin in the presence of titanium(III) citrate were investigated at pH 8 and 22 °C. Acetylene quantitatively reacted to ethene via vinylcobalamin as the proposed intermediate. Chloroacetylene reacted to acetylene and vinyl chloride. Proposed intermediates are ethynylcobalamin and vinylcobalamin; respectively. The principal initial reaction of chloroacetylene formed ethynylcobalamin which decomposed to acetylene. The proposition for ethynyl- and vinylcobalamin formation is based on fitting reaction models to kinetic data. Kinetic modeling suggests half-lives for ethynyl- and vinylcobalamin of 1.4 and 251 h, respectively. 1,1-Dichloroethene reacted to approximately 20% volatiles (ethane, ethane, vinyl chloride, and acetylene) and 80% unidentified nonvolatile products. cis- and trans-DCE transformed slowly end produced small yields of vinyl chloride, ethene, and ethane. The transformations of acetylene, chloroacetylene, 1,1-dichloroethene (DCE), and cis- and trans-DCE mediated by cobalamin in the presence of titanium(III) citrate were investigated at pH 8 and 22 °C. Acetylene quantitatively reacted to ethene via vinylcobalamin as the proposed intermediate. Chloroacetylene reacted to acetylene and vinyl chloride. Proposed intermediates are ethynylcobalamin and vinylcobalamin, respectively. The principal initial reaction of chloroacetylene formed ethynylcobalamin which decomposed to acetylene. The proposition for ethynyl- and vinylcobalamin formation is based on fitting reaction models to kinetic data. Kinetic modeling suggests half-lives for ethynyl- and vinylcobalamin of 1.4 and 251 h, respectively. 1,1-Dichloroethene reacted to approximately 20% volatiles (ethene, ethane, vinyl chloride, and acetylene) and 80% unidentified nonvolatile products. cis- and trans-DCE transformed slowly and produced small yields of vinyl chloride, ethene, and ethane.
- Semadeni, Marco,Chiu, Pei-Chun,Reinhard, Martin
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- Distribution of Rotational States in Half-Collisions: 193-nm Photolysis of Dichloroethylene
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The photodissociation of cis-, trans-, and 1,1-dichloroethylene (DCE) was studied by a pump-and-probe technique, using a 193-nm excimer laser to excite the parent molecule and time-of-flight resonance-enhanced multiphoton ionization to detect the products.We report here the nascent rotational state distributions of HCl(v''=0,1,2) and also the relative yields and intensity dependencies of HCl, H, Cl(2P3/2), Cl(2P1/2), HCl+, and Cl+.Our finding that the rotational state distributions of HCl for all three isomers are very similar leads us to conclude that the nascent distribution is determined far along the reaction coordinate and is insensitive to the isomeric for of the parent molecule, regardless of whether photoelimination results from a three- or four-center transition state.We also observed qualitatively different behavior for HCl(v''=0) and HCl(v''=1,2).As in our previous study of vinyl chloride, we found that HCl(v'>0) has a Boltzmann-like rotational state distribution, with temperatures in this case near 1400 K, whereas the distribution for v''=0 is described by a biexponential function with a low J'' temperature around 300 K and a high J'' temperature around 10000 K.We propose that the dichotomy between these two distributions is due to microscopic rather than chemical branching.The relative yields of HCl and Cl+ for trans-DCE are approximately double those of cis- and 1,1-DCE.This result is consistent with the interpretation that the yield-determining step is faster than cis-trans isomerization.The yields of all the other products are the same for cis and trans.For 1,1-DCE the yields of H, Cl(2P1/2), and HCl+ are much greater than for cis- and trans-DCE, while for Cl(2P3/2) the 1,1-DCE yield is somewhat smaller.The relative yields of H and Cl(2P3/2) can be explained by the stabilities of the organic fragments, while the HCl+ yields can be explained statistically.All of the neutral fragments were found to be produced by single-photon process, while HCl+ and Cl+ require three and four photons, respectively.Ladder climbing mechanisms are proposed for the two ionic framgents.
- He, Guo-xin,Yang, Yung-an,Huang, Yibo,Gordon, Robert J.
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- Shelf-Stable (E)- A nd (Z)-Vinyl-λ3-chlorane: A Stereospecific Hyper-vinylating Agent
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We report the first stereoselective synthesis of stable (E)- A nd (Z)-β-chlorovinyl-λ3-chlorane via direct mesitylation of 1,2-dichloroethylene with mesityldiazonium tetrakis(pentafluorophenyl)borate under mild reaction conditions. The structure of the (E)-vinyl-λ3-chlorane was established by single-crystal X-ray analysis. Because of the enormously high leaving group ability of the aryl-λ3-chloranyl group, vinyl-λ3-chloranes undergo not only SNVσ-type reaction with extremely weak nucleophiles such as perfluoroalkanesulfonate, iodobenzene, and aromatic hydrocarbons but also coupling with phenylcopper(I) species.
- Kanazawa, Junichiro,Miyamoto, Kazunori,Takagi, Taisei,Uchiyama, Masanobu,Watanabe, Yuichiro
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supporting information
p. 3469 - 3473
(2020/04/30)
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- Metal ions do not play a direct role in the formation of carbon-carbon triple bonds during reduction of trihaloalkyls by CrII or V II
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Carbyne radicals: Reactions of trihaloalkyl compounds with Cr2+ or V2+ in aqueous solutions yield alkynes and other products. Stepwise halogen abstractions from the trihaloalkyls form alkyl carbyne triradicals in solution. These radicals undergo coupling reactions, producing triply bonded alkyne molecules (see scheme). This process is not metal-assisted and does not occur in the coordination sphere of the metal ions.
- Levy, Ophir,Bino, Avi
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supporting information
p. 15944 - 15947
(2013/02/23)
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- GASEOUS DIELECTRICS WITH LOW GLOBAL WARMING POTENTIALS
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A dielectric gaseous compound which exhibits the following properties: a boiling point in the range between about ?20° C. to about ?273° C.; non-ozone depleting; a GWP less than about 22,200; chemical stability, as measured by a negative standard enthalpy of formation (dHf0); a toxicity level such that when the dielectric gas leaks, the effective diluted concentration does not exceed its PEL; and a dielectric strength greater than air.
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- ArF laser photolytic deposition and thermal modification of an ultrafine chlorohydrocarbon
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MW ArF laser irradiation of gaseous cis-dichloroethene results in fast decomposition of this compound and in deposition of solid ultrafine Cl- and H-containing carbonaceous powder which is of interest due to its sub-microscopic structure and possible reactive modification of the C-Cl bonds. The product was characterized by electron microscopy, and FTIR and Raman spectra and it was revealed that HCl, H2, and C/H fragments are lost and graphitic features are adopted upon heating to 700°C.
- Pola, Josef,Galikova, Anna,Subrt, Jan,Ouchi, Akihiko
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experimental part
p. 625 - 629
(2011/10/19)
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- Conformational product control in the low-temperature photochemistry of cyclopropylcarbenes
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Different conformers of two fused-ring cyclopropylchlorocarbenes are shown to undergo distinct, wavelength-selectable, photochemistry in low-temperature matrixes. Conformers with H and Cl syn give ring expansion predominantly, whereas those with H and Cl anti mainly fragment.
- Zuev, Peter S.,Sheridan, Robert S.,Sauers, Ronald R.,Moss, Robert A.,Chu, Gaosheng
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p. 4963 - 4966
(2007/10/03)
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- Photolysis of matrix-isolated fumaryl and maleoyl dichloride: Trapping of C4O2 and further evolutions
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The photochemical behavior of fumaryl and maleoyl dichloride, 1, respectively 2, in cryogenic matrix was investigated by means of FTIR spectroscopy. Irradiation of 1 with λ = 340 μm (n-π* band) led to a photoisomerization process, 1 →2, while irradiation of both compounds with λ = 260 μm (π -π* band) determined a complex process ending chloroethyne. C4O2 and C 3O are characterized as reaction intermediates. The transition states for the main reactions were localized at the HF/6-31g*//HF/6-31g* level, supporting the mechanism established on experimental grounds.
- Ionescu, Andrei,Petri, Nathalie,Monnier, Maurice,Hillebrand, Mihaela,Aycard, Jean Pierre
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- Pathways of chlorinated ethylene and chlorinated acetylene reaction with Zn(O)
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To successfully design treatment systems relying on reactions of chlorocarbons with zero-valent metals, information is needed concerning the kinetics and pathways through which transformations occur. In this study, pathways of chlorinated ethylene reaction with Zn(O) have been elucidated through batch experiments. Data for parent compound disappearance and product appearance were fit to pseudo-first-order rate expressions in order to develop a complete kinetic model. Results indicate that reductive β- elimination plays an important role, accounting for 15% of tetrachloroethylene (PCE), 30% of trichloroethylene (TCE), 85% of cis- dichloroethylene (cis-DCE), and 95% of trans-dichloroethylene (trans-DCE) reaction. The fraction of PCE, TCE, trans-DCE, and cis-DCE transformation that occurs via reductive elimination increases as the two-electron reduction potential (E2) for this reaction becomes more favorable relative to hydrogenolysis. In the case of PCE and TCE, reductive elimination gives rise to chlorinated acetylenes. Chloroacetylene and dichloroacetylene were synthesized and found to react rapidly with zinc, displaying products consistent' with both hydrogenolysis and reduction of the triple bond. Surface area-normalized rate constants (k(SA))for chlorinated ethylene disappearance correlate well with both one-electron (E1) and two-electron (E2) reduction potentials for the appropriate reactions. Correlation with E2 allows prediction of the distribution of reaction products as well as the rate of disappearance of the parent compound. To successfully design treatment systems relying on reactions of chlorocarbons with zero-valent metals, information is needed concerning the kinetics and pathways through which transformations occur. In this study, pathways of chlorinated ethylene reaction with Zn(0) have been elucidated through batch experiments. Data for parent compound disappearance and product appearance were fit to pseudo-first-order rate expressions in order to develop a complete kinetic model. Results indicate that reductive β-elimination plays an important role, accounting for 15% of tetrachloroethylene (PCE), 30% of trichloroethylene (TCE), 85% of cis-dichloroethylene (cis-DCE), and 95% of trans-dichloroethylene (trans-DCE) reaction. The fraction of PCE, TCE, trans-DCE, and cis-DCE transformation that occurs via reductive elimination increases as the two-electron reduction potential (E2) for this reaction becomes more favorable relative to hydrogenolysis. In the case of PCE and TCE, reductive elimination gives rise to chlorinated acetylenes. Chloroacetylene and dichloroacetylene were synthesized and found to react rapidly with zinc, displaying products consistent with both hydrogenolysis and reduction of the triple bond. Surface area-normalized rate constants (kSA) for chlorinated ethylene disappearance correlate well with both one-electron (E1) and two-electron (E2) reduction potentials for the appropriate reactions. Correlation with E2 allows prediction of the distribution of reaction products as well as the rate of disappearance of the parent compound.
- Arnold, William A.,Lynn Roberts
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p. 3017 - 3025
(2007/10/03)
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- Intramolecular Geminal and Vicinal Element Effects in Substitution of Simple Bromo(chloro)alkenes by Methoxide and Thiolate Ions. An Example of a Single Step Substitution?
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Intramolecular element effects kBr/kCl for substitution of geminal bromochloroalkenes BrC(Cl)=C-(Br)Cl (1), BrC(Cl)=CCl2 (2), Me2C=C(Br)Cl (3), and XCH=C(Br)Cl (X = Cl, 4; X = Br, 5), with MeO- and RS- nucleophiles were investigated. 3 did not give substitution, and 4 and 5 gave substitution with MeO- via an initial elimination (to acetylene)-addition route, followed by further reactions. In reactions of 4 with thiolates, geminal element effects of 2-10 were obtained. Formation of RSC(Cl)=C(Cl)Y, Y = SR, Br, is ascribed to an initial halophilic reaction, followed by addition of RSCl to the formed acetylene. Reaction of 2 with MeO- gave a high vicinal element effect, and RS- gave a high geminal element effect. Reaction of 1 with both MeO- and RS- ions gave high (2 orders of magnitude) geminal element effects, which were interpreted as indicating a rate-determining C-X bond cleavage. This is supported by the high kBr/kCl intermolecular element effects (k(1)/k(Cl2C=CCl2) with MeO- and PhCH2S- ions. Mechanistic alternatives based on these observations are discussed.
- Beit-Yannai, Michal,Rappoport, Zvi,Shainyan, Bagrat A.,Danilevich, Yuri S.
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p. 8049 - 8057
(2007/10/03)
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- Hydrogen-Atom-Induced Decomposition of Trichloroethylene at High Temperatures
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Mechanisms and rate constants for hydrogen atom attack on trichloroethylene have been determined in single-pulse shock tube experiments near 1050 K.Products from all the decomposition channels have been observed.The predominant process is the displacement of the chlorine at the least substituted site.The following rate expressions have been determined: k(H* + HClC=CCl2 -> H2C=CCl2 + Cl*) = 6 x 1E13 exp(-2439/T) cm3 mol-1 s-1; k(H* + HClC=CCl2 -> HClC=CClH (cis + trans) + Cl*) = 3.7 x 1E13 exp(-3946/T) cm3 mol-1 s-1; k(H* + HClC=CCl2 -> *HC=CCl2 or HClC=CCl* + HCl) = 3.8 x 1E14 exp(-6686/T) cm3 mol-1 s-1.An upper limit for the rate constant of the abstraction process H* + HClC=CCl2 -> *ClC=CCl2 + H2 is 6.5 x 1E10 cm3 mol-1 s-1 at 1050 K.Rate constants for chlorine attack on H2 at these temperatures are a factor of 13 smaller than those on mesitylene.The results are compared with those for hydrogen atom reactions with other unsaturated compounds.Some implications regarding the incineration of chlorinated organics will be discussed.
- Tsang, Wing,Walker, James A.
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p. 3156 - 3161
(2007/10/02)
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- Small Rings, 83. - C3F2 Isomers: Generation by Pulsed Flash Pyrolysis and Matrix-Spectroscopic Identification
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Matrix-isolated difluorovinylidenecarbene (4) has been generated by pulsed flash pyrolysis from 1-chloro-3,3-difluorocyclopropene (8a) and 3,3-difluoro-1,2-diiodocyclopropene (8b).By subsequent photolysis 4 isomerizes to difluoropropargylene (5) and difluorocyclopropenylidene (6).The identification of the three new carbenes is based on the comparison of their experimental and calculated (MP2/6-31G*) infrared spectra. - Key Words: Matrix isolation / Photochemistry / Flash pyrolysis / Carbenes
- Maier, Guenther,Preiss, Thomas,Reisenauer, Hans Peter
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p. 779 - 782
(2007/10/02)
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- The Infrared Spectrum of Chlorophosphaethyne, ClCP
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C-Chlorophosphaethyne (ClCP) has been generated by the pyrolysis of Cl3CPCl2 over granulated zinc at 550 deg C and the high-resolution spectrum in the region 4000-100 cm-1 has been recorded, analyzed, and assigned.Altogether, more than 6500 transitions have been assigned.The observed bands include all three fundamentals as well as number of overtone, combination, and difference bands.For all the bands both the 35Cl and 37Cl isotopomers were observed, and for the ν3 band the 35Cl13C isotopomer was observed in natural abundance.The ground state rotation constants B0 and distorsion constants D0 were found to be 0.10074626(10) and 1.2544(10)E-8 cm-1 and 0.0981080(14) and 1.1950(16)E-8 cm-1 for the 35Cl and 37Cl isotopomers, respectively, and 0.10073766(72) and 1.158(11)E-8 cm-1 for the 13C species.After accounting for Fermi resonance effects the vibration-rotation parameters, αi, for all three fundamentals have been estimated and used to calculate the equilibrium B values; Be = 0.10094715(89) and 0.09830590(100) for the 35Cl and 37Cl isotopomers, respectively.The equilibrium geometry is calculated to be rCP=155.26(61) and rC-Cl=163.41(62) pm.The available fundamental frequencies for all three isotopomers have been used to calculate the harmonic force constants: fR(C-Cl)- 4.621; fr(CP)=9.033; fRr=0.499 aJ Angstroem-2; and fα=0.348 aJ.
- Naughton, D. Mc,Bruget, D. N.
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p. 336 - 350
(2007/10/02)
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- Kinetics of the Competitive 1,2-Carbon Migrations of an Unsymmetrically Substituted Cyclopropylchlorocarbene
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Photolysis of 3-(2,2-dimethylcyclopropyl)-3-chlorodiazirine (4) at 25 deg C in pentane affords 81 percent of the 1,2-C migration products 1-chloro-3,3-dimethylcyclobutene (5) and 2-chloro-3,3-dimethylcyclobutene in a 4.8:1 distribution, as well as 19 percent of the fragmentation products, isobutene, and chloroacetylene.Experiments in the presence of the carbene trap trimethylethylene point to product formation from the electronically excited diazirine (4*), which affords 19-20 percent of fragmentation products, ca. 17 percent of 5 and 6 (3.8:1), and ca. 63 percent of 2,2-dimethylcyclopropylchlorocarbene (3).The carbene ring expands to 5 and 6 (5.2:1).Laser flash photolytic studies afford absolute rate constants for 3 -> 5 (1.3 * 106 s-1) and 3 -> 6 (2.5 * 105 s-1).The 5-fold preference of 3 for CH2 migration (to 5) over CMe2 migration (to 6) is attributed to differential steric affects.Ab initio calculations afford structures and energies for 3 and the CH2 and CMe2 transition state (8-CH2 and 8-CMe2).The calculations agree with the experimental findings in that ΔG* for CH2 migration is found to be 1.4 kcal/mol less than ΔG* for CMe2 migration, corresponding to a computed 10-fold kinetic preference for CH2 migration.The expected additional steric congestion is apparent in the 8-CMe2 transition state.
- Moss, Robert A.,Liu, Weiguo,Krogh-Jespersen, Karsten
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p. 13413 - 13418
(2007/10/02)
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- A practical synthesis of chloroacetylene via phase-transfer catalysis
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Chloroacetylene (1) was synthesized as solution in hexane from 1,1-dichloroethene (2) in the presence of 50% aqueous sodium hydroxide and tetrabutylammonium hydrogen sulfate as a catalyst (PTC), in moderate yield. Reaction of 2-phenylpropiononitrile with 1 afforded the corresponding 3-butynenitrile 3 in good yield.
- Kulinski,Jonczyk
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p. 757 - 758
(2007/10/02)
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- Kinetics of reactions of chlorinated vinyl radicals CH2CCl and C2Cl3 with molecular oxygen
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The kinetics of the reactions of CH2CCl and C2Cl3 radicals with O2 have been studied in a tubular flow reactor coupled to a photoionization mass spectrometer in the temperature range 298-648 K. Radicals were produced by the homogeneous photolysis of a suitable precursor using an excimer laser. The observed or indicated reaction mechanisms as well as the rate constants, which were measured as a function of density and temperature, suggest that both of these reactions proceed via the formation of a short-lived bound RO2 intermediate that can either decompose back to the original reactants or form new oxygen-containing products following internal rearrangement of the adduct.
- Russell,Seetula,Gutman,Senkan
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p. 1934 - 1938
(2007/10/02)
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- CHLOROVINYLATION OF BENZENESELENOL AND ORGANIC DISELENIDES BY CHLORO- AND DICHLOROACETYLENES
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Mixtures of the Z and E isomers of unsaturated organic selenides and 1,2-bis(organoseleno)mono(di)chloroethylenes were obtained by the addition of benzeneselenol and organic diselenides to the etherates of chloro- and dichloroacetylene
- Martynov, A. V.,Mirskova, A. N.,Voronkov, M. G.
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p. 1326 - 1328
(2007/10/02)
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- Pulse-Duration Effects on Competitive Reactions in Infrared Multiple-Photon Decomposition of CH2ClCHClF and CHClFCHClF
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Vibrationally excited 1,2-dichlorofluoroethane and 1,2-dichloro-1,2-difluoroethane have been observed to dissociate competitively via two channels to form vibrationally excited HCl and HF.The fluence dependences of the branching ratio have been measured for both "short"-pulse (80-ns fwhm) and "long"-pulse (80-ns fwhm with 1-μs-fwhm tail) irradiations.The branching ratio shows not only fluence dependence but also pulse-duration dependence, that is, intensity dependence.When the reactant pressure is 1.0 Torr, collisional deactivation is expected to occur to a considerable extent under long-pulse irradiation while it can be ignored under short-pulse irradiation.The experimental results are interpreted by using the exact stochastic method based on the energy-grained master equations, which take into account collisional deactivation.
- Ishikawa, Yo-ichi,Sugita, Kyoko,Arai, Shigeyoshi
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p. 5067 - 5071
(2007/10/02)
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- CO2 Laser-induced Decomposition of 1,2-Dichloro-1-fluoroethane
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CH2ClCHFCl was photolyzed with a TEA CO2 laser at 1033.5 cm-1.The infrared multiphoton dissociation mechanism of CH2ClCHFCl was investigated under various conditions: Sample gas pressure, additive gas presure, pulse number, pulse energy, and pulse duration.It is concluded that primary process of the IRMPD is direct eleimination of molecular HCl and HF, HCl elimination being predominant channel.Primary HCl elimination products cis-and trans-CHF=CHCl, and CH2=CFCl are formed at high vibrational levels, from which additional photon absorption occures in the secondary photolysis to give rise to CH=CCl, CH=CF, and CH2=CHF.All of the secondary products are concluded to be derived from mainly CH2=CFCl among the chlorofluoroethene isomers.CH2=CFCl decomposes via HF and HCl elimination channels together with the C-Cl bond repture channel. appears to be generated by the H atom abstraction reaction of C2H. radical, which may result from further decomposition of and/or .The neat IRMPD at higher pressures gives quite similar primary product distribution, but markedly different secondary product distribution from those in shock tube pyrolysis.
- Ogura, Hiroo,Yano, Takayuki
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p. 1239 - 1250
(2007/10/02)
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- Infrared Multiphoton Decomposition of 1-Chloro-1-fluoroethene
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Unimolecular dissociation and subsequent reactions of CH2=CFCl subjected to the infrared multiphoton excitation were studied with a focused geometry using the P(10) line of the 10.6 μm CO2 band at 952.9 cm-1.The final products of the photolysis observed were CH=CCl, CH=CF, CH=CH, CH2CHF, and CH2=CF2.A series of diagnostic experiments shows that the primary processes of photolysis involve the molecular elimation of HF and HCl, to minor extend C-Cl bond rupture.The relative importance of the primary steps is tentatively estimated to be approximately 100:65:25, respectively.Primarily formed CH=CCl and CH=CF suffer from secondary photolysis absorbing additional photons.More fraction of CH=CF primary yield is decomposed than that of CH=CCl, due to the accidental resonance with the laser excitation line.CH=CH and CH2=CHF are concluded to be formed by the H atom abstraction reaction of CH2=C. and CH=CF. radicals generated during the photolysis respectively, CH2=CF2 beging formed by the recombination reaction between CH2=CF. radical and F atom.In the shock tube pyrolysis the formation of CH=CF predominates over that of CH=CCl.A mechanistic change to form CH=CF in the shock tube pyrolysis is suggested.
- Ogura, Hiroo
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p. 1358 - 1366
(2007/10/02)
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- CO2 Laser-induced Decomposition of 1,1,2-Trichloroethane
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CH2ClCHCl2 was photolyzed with a focusing geometry using the P(24) line of the 10.6 μm CO2 band (940.6 cm-1).The final products of neat photolysis were cis- and trans-CHCl=CHCl, CH2=CCl2, CH2=CHCl, CHCCl, CHCH, and C4H2.The relative yield of CH2=CCl2 in particular was strongly dependent on CH2ClCHCl2 pressure and sensitive to the addition of H atom containing molecules.A series of diagnostic experiments shows that the dichloroethene isomers are formed by three different processes, i.e., infrared multiphoton decomposition, collision-induced decomposition, and radical chain reaction.Infrared multiphoton decomposition and collision-induced decomposition give rise to cis- and trans-CHCl=CHCl predominantly, while the radical chain reaction generates the dichloroethane isomers in comparable amounts at high reactant pressures, the most probable initiation step being the C-Cl bond-scission reaction of the parent molecule.Formation mechanisms for other minor products are also discussed.
- Ogura, Hiroo
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p. 3528 - 3534
(2007/10/02)
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- Infrared Laser Multiphoton Dissociation of CF2ClCH2Cl
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The infrared multiphoton decomposition (IRMPD) of CF2ClCH2Cl was studied with focusing geometry using the P(34) line of the 9.6-μm CO2 band (1033.6 cm-1).The principal reaction product is CF2CHCl.Other products of significance include CFClCHCl, CF2CH2, and CFCH.It is concluded that the primary processes of photodecomposition involve the molecular elimination of HCl and HF and, to a very minor extent, C-C bond rupture.The relative importance of the primary steps is approximately 1000:30:1, respectively.From a series of diagnostic experiments in the presence of hydrogen donors and D2, it is shown that CF2CH2 derives from the secondary photolysis of CF2CHCl.The decomposition yield, the HF/HCl ratio, and the CF2CH2/CF2CHCl ratio were investigated as a function of reactant and argon pressure, the latter serving as a buffer gas.From the dependence of the decomposition yield on pulse number at different pulse energies, E0, the specific rate of decomposition, b, was found to be proportional to b E01.8, the power dependence being somewhat higher than the standard 3/2 power law for focusing geometry.These phenomena are interpreted in terms of a simple geometric fluence model which includes contributions from collisionally induced reactions in the outermost (lower fluence) irradiated region.The nonresonant photodecomposition of C2H6 and C2H4 at 1033.6 cm-1 observed in auxiliary, diagnostic experiments is interpreted in terms of photosensitization processes.
- Yano, T.,Ozaki, S.,Ogura, H.,Tschuikow-Roux, E.
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p. 1108 - 1116
(2007/10/02)
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- Determination of Arrhenius parameters for unimolecular reactions of chloroalkanes by IR laser pyrolysis
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A simple and reliable method is elaborated for accurate measurements of thermal rate constants of homogeneous gas phase unimolecular reactions.A pulse of CO2 laser radiation was used to multiphoton excite SiF4 sensitizer molecules and consequently produce temperatures in the range 1100-1400 K.Expansion of the heated gas column quenches pyrolysis reactions on a 10 μs time scale.There are no hot surfaces to induce chemistry.HCl elimination from C2H5Cl, Ea = 57.4 kcal/mol and log A(s-1) = 13.8, was used as an internal temperature standerd.For the molecular elimination CCL3CH3 -> HCl + CCl2CH2, Ea = 49.5 +/- 1.3 kcal/mol and log A(s-1) = 13.1 +/- 0.3, were determined.In these experiments the major decomposition products of CHCl2CH2Cl are HCl and cis- or trans-CHClCHCl with Ea = 58.5 +/-2, log A = 14.1 +/- 0.4 and Ea = 59.5 +/- 2, log A = 13.9 +/- 0.4, respectively.HCl elimination to give CCl2CH2 and C-Cl bond breaking to CHClCH2Cl radical have higher activation energies.The method is generally useful for kinetics at high temperature.
- Dai, Hai-Lung,Specht, Eliot,Berman, Michael R.,Moore, C. Bradley
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p. 4494 - 4506
(2007/10/02)
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- Infrared Spectra of Hydrogen-Bonded ? Complexes between Hydrogen Halides and Acetylene
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Hydrogen-bonded ? complexes C2H2--H-X have been formed by codeposition of C2H2 and HX in excess argon at 15 K and by vacuum-UV photolysis of vinyl halides.The strength of the hydrogen bond, as measured by the displacement of the H-X vibrational fundamental below the isolated HX value, decreases in the series HF, HCl, and HBr as expected.Similar complexes made from di- and thichloroethylenes give slightly higher H-Cl vibrations which show minimal interaction between the halide and the acetylene substituent.The H-F fundamentals for C2H4 and C2H2 complexes at 3732 and 3747 cm-1, respectively, show that the ? electrons in double and triple bonds are comparable hydrogen-bond acceptors.
- McDonald, Stephen A.,Johnson, Gary L.,Keelan, Brian W.,Andrews, Lester
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p. 2892 - 2896
(2007/10/02)
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- Competing Pathways in the Infrared Laser Photolysis of 1-Chloro-1-fluoroethylene
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The multiphoton-induced decomposition of 1-chloro-1-fluoroethylene (CH2CClF) and the effect of laser fluence upon the decomposition pathways has been investigated by using a pulsed TEA CO2 laser operating at 10.632 μm.CH2CClF has been found to decompose via two competing pathways, yielding either HF and HCCCl or HCl and HCCf.The decomposition reactions have been followedin real time by monitoring the IR fluorescence from the vibrationally excited HF and HCl.Variation of the laser fluence causes the HF/HCl product ratio to change.This change is explained in terms of a competition between the reaction pathways and the optical pumping rate.
- Jalenak, W. A.,Nogar, N. S.
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p. 2993 - 2995
(2007/10/02)
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- EFFECT OF HYDROGEN CHLORIDE ON THE PYROLYSIS OF ACETYLENE AS STUDIED WITH A SINGLE-PULSE SHOCK TUBE.
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The hydrocarbons produced in the C//2H//2-HCl system were quite the same as those obtained in the C//2H//2-Ar system. The formation rate of the main pyrolysis product, 1-buten-3-yne, was reduced remarkably by the addition of hydrogen chloride, being of third-order and of inverse first-order with respect to the concentrations of acetylene and hydrogen chloride, respectively. As the chlorine atom containing product, only chloroacetylene was found in small amounts, its formation rate being of second-order with respect to acetylene. The inhibitory effect of hydrogen chloride on the 1-buten-3-yne formation rate was interpreted in terms of the change in the termination from the recombination reaction of 2-ethynylvinyl radical to the reaction of 2-ethynylvinyl radical with hydrogen chloride.
- Ogura
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p. 1210 - 1215
(2007/10/02)
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