871-28-3

At 298 K the reactions of 2,5-dimethlyfuran + CH(X2Θ) and + CD radicals were investigated using synchrotron radiation coupled with multiplexed photoionization mass spectrometry at the Lawrence Berkeley National Laboratory. Reaction products wer

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.

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.

The photochemistry of cyclopentadiene isolated in low-temperature argon matrices was studied by means of IR and UV/VIS spectroscopy. Bicyclo[2.1.0]pent-2-ene was formed by the irradiation of matrix-isolated cyclopentadiene using a super-high-pressure mercury lamp. When the matrix-isolated cyclopentadiene was irradiated with shorter wavelength using a low-pressure mercury lamp, further reactions of bicyclo[2.1.0]pent-2-ene were found to produce allylacetylene and vinylallene. While the photochemistry of cyclopentadiene to form bicyclo[2.1.0]pent-2-ene is known in a solution system, the production of allylacetylene and vinylallene in a matrix-isolated system has never been previously reported. The assignments of the species and the determination of the reaction mechanisms were performed using molecular orbital calculations.

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The gas phase pyrolysis of cyclopropylacetylene (3) has been investigated in a flow system between 600 and 900 deg C.At the lower temperature limit 3 isomerizes to give 1,2,4-pentatriene (9), cis- (10) and trans-3-penten-1-yne (11), as well as 1-penten-4-yne (12), all isomers being formed in roughly equal amounts.At 850 deg C none of these C5H6-hydrocarbons is formed; rather, 1,3-cyclopentadiene (13), benzene (14), toluene (15), indene (16), naphthalene (17), and acenaphthylene (18) are the major constituents of a complex pyrolysate.The mechanisms of formation of the major pyrolysis products are discussed.

The photobehavior of the acyclic vinyl iodide 2, the 1-iodocycloalkenes 11-14 and 39, the (halomethylene)cycloalkanes 45-48, and the (dihalomethylene)cyclohexanes 62-64 has been studied.Except for the dichloride 64, which exhibited only radical behavior, each of the halides afforded a mixture of ionic and radical products.The two bromides studied, 48 and 63, afforded lower ratios of ionic to radical products than the corresponding iodides 45 and 62.Irradiation of vinyl iodides was found to be a convenient and powerful method for the generation of vinyl cations, including the highly strained 1-cyclohexenyl and 1-cyclopentenyl cations and the unstabilized α-unsubstituted cations 51 and 54.The latter cations underwent rearrangement to the ring-expanded 1-cycloalkenyl cations 28 and 36, respectively.Lowering the temperature of the irradiation of iodides 13, 14, and 45 resulted in an increased ratio of ionic to radical products.However, iodide 47, which underwent principally fragmentation to enyne 61, showed little temperature effect.