- Photodissociation dynamics of the allyl radical
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The photochemistry and photodissociation dynamics of the allyl radical upon ultraviolet (UV) excitation is investigated in a molecular beam by using time- and frequency-resolved photoionization of hydrogen atoms with Lyman-a-radiation. The UV states of allyl decay by internal conversion to the ground state, forming vibrationally hot radicals that lose hydrogen atoms on a nanosecond time scale. Two channels are identified, formation of allene directly from allyl, and isomerization from allyl to 2-propenyl, with a subsequent hydrogen loss, resulting in both allene and propyne formation. The branching ratio is between 2:1 and 3:1, with direct formation of allene being the dominant reaction channel. This channel is associated with site-selective loss of hydrogen from the central carbon atom, as observed in experiments on isotopically labeled radicals. Ab initio calculations of the reaction pathways and Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the rates are in agreement with the mechanism and branching ratios. From the measured Doppler profiles a translational energy release of 14±1 kcal/mol is calculated. The calculated value of 66 kcal/mol for the barrier to the 1,2 hydrogen shift from allyl radical to 2-propenyl is confirmed by the experimental data.
- Deyerl, Hans-Juergen,Fischer, Ingo,Chen, Peter
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- Kinetics and dynamics in the photodissociation of the allyl radical
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The direct observation of the products, kinetics and translational energy release from the photodissociation of the allyl radical, C3H5, upon excitation in the near-uv is reported. A statistical analysis of the data shows that they are in agreement with allene formation being the dominant H-loss reaction channel.
- Deyerl, Hans-Juergen,Gilbert, Thomas,Fischer, Ingo,Chen, Peter
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- Photocycloadditions of tetrachloro-1,4-benzoquinone (chloranil) onto cyclobutene and cyclopropene. Expected and unexpected products
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Solutions of chloranil (CA) in chlorobenzene were irradiated in the presence of cyclobutene and cyclopropene. Cyclobutene gave rise to two conventional 1:2 cycloadducts onto the dichloroethene subunits of CA and an α,β-unsaturated α,γ-dichloro-γ-lactone. Heating of the crude product in methanol converted the lactone into an α,β- unsaturated methyl γ-oxocarboxylate (25% yield) and a large amount of the major 1:2 cycloadduct, which contains chlorocyclobutane entities, into a cyclopropylcarbinyl chloride derivative (24% yield). An entirely new product type was the result in the case of cyclopropene. After treatment of the crude product with methanol a tetracyclic acetal containing a cyclopentanone and a dihydropyran subunit was isolated in 36% yield. Apparently, CA had taken up two molecules of cyclopropene. One of the resulting cyclopropane entities must have undergone a rearrangement en route to the final product.
- Braun, Max,Christl, Manfred
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- Stereo- and Regioselective 1,3-Dipolar Cycloaddition of the Stable Ninhydrin-Derived Azomethine Ylide to Cyclopropenes: Trapping of Unstable Cyclopropene Dipolarophiles
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A stereo- and regioselective 1,3-dipolar cycloaddition of the stable ninhydrin-derived azomethine ylide [2-(3,4-dihydro-2H-pyrrolium-1-yl)-1-oxo-1H-inden-3-olate, DHPO] to differently substituted cyclopropenes has been established. As a result, an efficient synthetic protocol was developed for the preparation of biologically relevant spiro[cyclopropa[a]pyrrolizine-2,2′-indene] derivatives. DHPO has proved to be an effective trap for such highly reactive and unstable substrates as parent cyclopropene, 1-methylcyclopropene, 1-phenylcyclopropene, and 1-halo-2-phenylcyclopropenes. It has also been found that 3-nitro-1,2-diphenylcyclopropene undergoes a nucleophilic substitution reaction in alcohols and thiols to afford 3-alkoxy- and 3-arylthio-substituted 1,2-diphenylcyclopropenes, which can be captured as corresponding 1,3-dipolar cycloadducts in the presence of DHPO. These new approaches provide a straightforward strategy for the synthesis of functionally substituted cyclopropa[a]pyrrolizine derivatives. The factors governing regio- and stereoselectivity have been revealed by means of quantum mechanical calculations (M11 density functional theory), including previously unreported Nylide-Hcyclopropene second-orbital interactions. The outcome of this work contributes to the study of 1,3-dipolar cycloaddition, as well as enriches chemistry of cyclopropenes and methods for the construction of polycyclic compounds with cyclopropane fragments.
- Filatov, Alexander S.,Wang, Siqi,Khoroshilova, Olesya V.,Lozovskiy, Stanislav V.,Larina, Anna G.,Boitsov, Vitali M.,Stepakov, Alexander V.
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p. 7017 - 7036
(2019/06/14)
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- CYCLOPROPENES-GENERATING DEVICES TO CONTROL RIPENING PROCESSES OF AGRICULTURAL PRODUCTS
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Provided is a device for generation of cyclopropene compounds which is capable of achieving direct in situ preparation and application of cyclopropene compounds inhibiting the action of ethylene which accelerates the ripening process of plants, the device comprising a first storage part for storing precursors of cyclopropene compounds (“cyclopropene precursors”), a second storage part for storing reaction reagents which convert cyclopropene precursors into cyclopropene derivatives via chemical reaction, and a spray part for spraying the cyclopropene derivatives produced by the chemical reaction between the cyclopropene precursors and the reaction reagents.
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Page/Page column 6
(2012/06/01)
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- Photoisomerization and photochemistry of matrix-isolated 3-furaldehyde
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3-Furaldehyde (3FA) was isolated in an argon matrix at 12 K and studied using FTIR spectroscopy and quantum chemistry. The molecule has two conformers, with trans and cis orientation of the O=C-C=C dihedral angle. At the B3LYP/6-311++G(d,p) level of theory, the trans form was computed to be ca. 4 kJ mol-1 more stable than the cis form. The relative stability of the two conformers was explained using the natural bond orbital (NBO) method. In fair agreement with their calculated relative energies and the high barrier of rotamerization (ca. 34 kJ mol-1 from trans to cis), the trans and cis conformers were trapped in an argon matrix from the compound room temperature gas phase in proportion ~7:1. The experimentally observed vibrational signatures of the two forms are in a good agreement with the theoretically calculated spectra. Broad-band UV-irradiation (λ > 234 nm) of the matrix-isolated compound resulted in partial trans → cis isomerization, which ended at a photostationary state with the trans/cis ratio being ca. 1.85:1. This result was interpreted based on results of time-dependent DFT calculations. Irradiation at higher energies (λ > 200 nm) led to decarbonylation of the compound, yielding furan, cyclopropene-3-carbaldehyde, and two C3H4 isomers: cyclopropene and propadiene.
- Kus, Nihal,Reva, Igor,Fausto, Rui
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scheme or table
p. 12427 - 12436
(2011/02/28)
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- Cyclic versus linear isomers produced by reaction of the methylidyne radical (CH) with small unsaturated hydrocarbons
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The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacety- lene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time- resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysisof CHBr 3 at 298 K and react with the selected hydrocarbon i n a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomer-specific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C 2 H 4 reaction the C 3 H 5 intermediate decays byH atom loss to yield 70(±8)percent allene, 30(±8)percent methylacetylene, and less than 10percent cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mai nly the cyclic C 3 H 2 isomer is contrary to a previous RRKM calculations that predicted linear triplet propargylene to be 90percent of the total H-atom coproducts. High-level CBS-APNO quantum calculations and RRKM calculations for the CH + C 2 H 2 reaction presented in this manuscript predict a higher contribution of the cyclic C 3 H 2 (27.0percent) versus triplet propargylene (63.5percent) than earlier predictions. Extensive calculations onthe C 3 H 3 and C 3 H 2 D system combined with experimental isotope ratios for the CD + C 2 H2 reaction indicate that H-atom-assisted isomerization in the present experiments is responsible for the remaining discrepancy between the new RRKM calculations and the experimental results. Cyclic isomers are also found to represent 30(±6)percent of the detected products in the case of CH + methylacetylene, together with 33(±6)percent 1,2,3- butatriene and 37(±6)percent vinylacetylene. The CH + allene reaction gives 23(±5)percent 1,2,3-butatriene and 77(±5)percent vinylacetylene, whereas cyclic isomers are produced below the detection limit in this reaction. The reaction exit channels deduced by comparing the product distributions for the aforementioned reactions are discussed in detail.
- Goulay, Fabien,Trevitt, Adam J.,Meloni, Giovanni,Selby, Talitha M.,Osborn, David L.,et al.
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experimental part
p. 993 - 1005
(2009/06/28)
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- Crossed beam investigations of the reaction dynamics of O(3P) with allyl radical, C3H5
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The nascent rovibrational distributions of the OH product from the newly observed exothermic reaction of O(3P)+C3H5→ C3H4+OH were studied. The atom-radical reaction dynamics was first probed through t
- Kwon, Han-Cheol,Park, Jong-Ho,Lee, Hohjai,Kim, Hee-Kyung,Choi, Young-Sang,Choi, Jong-Ho
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p. 2675 - 2679
(2007/10/03)
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- Intermolecular Pauson-Khand reactions of cyclopropane: A general synthesis of cyclopentanones
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(equation presented) The Pauson-Khand reaction of cyclopropene with a variety of terminal alkynes has been studied. The best reaction conditions involve NMO activation in CH2Cl2 at -35 °C. In this way, 3-substituted-bicyclo[3.1.0]hex-3-en-2-ones have been obtained in good to excellent yields. As a synthetic application, several types of substituted cyclopentenones have been prepared from these cycloadducts by protocols involving conjugate addition and reductive ring opening.
- Marchueta, Iolanda,Verdaguer, Xavier,Moyano, Albert,Pericas, Miquel A.,Riera, Antoni
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p. 3193 - 3196
(2007/10/03)
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- UV photodissociation dynamics of allyl radical by photofragment translational spectroscopy
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The photodissociation of the allyl radical was studied by photofragment translational spectroscopy following excitation to the C(pver-tilde) (22B1) and A(over-tilde)(12B1) states. At 248 nm excitation, two different primary channels were detected: H-atom loss and CH3 elimination. The overall shape of the P(ET) for the H-atom loss channel suggests a statistical dissociation from the ground potential energy surface of the C3H5 system.
- Stranges,Stemmler,Yang,Chesko,Suits,Lee
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p. 5372 - 5382
(2007/10/03)
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- Cyclopropene Photochemistry. Mechanistic and Exploratory Organic Photochemistry
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Four new cyclopropenes have been synthesized and their photochemistry has been investigated.Thus, 3-methyl-1,2-diphenyl-3-(2-phenylallyl)cyclopropene was found on direct photolysis to afford four photoproducts, the two major products of which derived from novel photochemistry. 2-Methylene-4-methyl-5,6-diphenyltetracyclo1,504,6>undeca-8,10-diene derived from cycloaddition of the excited cyclopropenyl ? bond to the C-1,C-2 ? bond of the phenyl of the 2-phenylallyl side chain.The quantum yield for this novel transformation was 0.023.A second photoproduct was 2-methyl-1,4,6-triphenyltricyclo2,6>hexane.This product results from a formal cycloaddition of the excited cyclopropenyl ? bond to the allyl double bond.A diradical mechanism is structurally equivalent.Formation of such a tricyclic 2,6> system is normally not found in direct irradiations.The quantum yield for this product was 0.088.Also formed was 3-methyl-1,2,5-triphenylbicyclohex-2-ene with an efficiency of 0.019.This product is understood as deriving either (i) from cyclopropene opening to a carbene which then adds to the allyl ? bond or (ii) from a bicyclic diradical arising from vinyl-vinyl bonding.The fourth photoproduct is 2-methyl-1,3-diphenyl-3-(2-phenylallyl)cyclopropene.The efficiency was 0.018.The bicyclic diradical above provides a common species leading to the last three products.Sensitization led only to the first two products: the tetracyclic diene (φ=0.26) and the tricyclo2,6>hexane (φ=0.15).Product structures were established by X-ray, degradation, independent synthesis, and spectral analysis.In addition, the photochemistry of cis- and trans-2,6-dimethyl-1,6-diphenylspirooct-1-ene was investigated.Stereoisomerization resulted from the singlet but not the triplet.Mechanisms for the above transformations are considered.Finally, corresponding thermal chemistry exhibited by the above compounds was investigated.
- Zimmerman, Howard E.,Bunce, Richard A.
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p. 3377 - 3396
(2007/10/02)
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- DESHYDROHALOGENATION EN PHASE VAPEUR D' HALOGENURES D' ALKYLES SUR t-BUTYLATE DE POTASSIUM SUPPORTE SUR SILICE: VOIE D' ACCES AUX CYCLES TRES TENDUS
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Heterogenous reactions: Highly strained cycloalkenes can be obtained by vapor phase dehydrohalogenation of halocycloalkanes over potassium t-butoxide supported by silica.
- Denis, J. M.,Niamayoua, R.,Vata, M.,Lablache-Combier, A.
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p. 515 - 518
(2007/10/02)
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- Thiono and Dithio Esters, XXV. - (4+2) Cycloadditions with Dithionooxalates
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O,O-Dimethyl dithiooxalate (1a) reacts as a 2?-component with typical dienes (e.g. 2,3-dimethylbutadiene or cyclopentadiene) as well as with the strained ?-bonds of quadricyclane to form cycloaddition products.With the energy-rich double bonds of norbornene derivatives, cyclopropenes, and benzovalene, 1a as a 4?-component furnishes cycloadducts.With cyclopentene an equilibrium of product and starting material was achieved after two weeks. 1a reacts also with substances containing activated triple bonds such as dehydrobenzene or acetylenedicarboxylic ester.
- Hartke, Klaus,Henssen, Guenter,Kissel, Thomas
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p. 1665 - 1676
(2007/10/02)
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