2873-50-9Relevant articles and documents
Cyclic versus linear isomers produced by reaction of the methylidyne radical (CH) with small unsaturated hydrocarbons
Goulay, Fabien,Trevitt, Adam J.,Meloni, Giovanni,Selby, Talitha M.,Osborn, David L.,et al.
experimental part, p. 993 - 1005 (2009/06/28)
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.
Photoisomerization of bicyclopropylidene and 1,2-dimethylenecyclobutane in rare-gas matrices: Towards the IR-spectroscopic identification of tetramethyleneethane (2,3-dimethylenebutane-1,4-diyl)
Maier, Guenther,Senger, Stefan
, p. 1291 - 1294 (2007/10/03)
Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm- 1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of k λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
The gasphase photolysis of 2-methy-1,3-butadiene at 123.6 nm
Lang, Valerie I.,Doepker, Richard D.
, p. 1731 - 1735 (2007/10/02)
The gas-phase photolysis of 2-methyl-1,3-butadiene has been investigated using krypton (123.6 nm) resonance radiation.The observed neutral products of the primary decomposition were vinylacetilene, ethylene, acetylene, methylacetylene, propylene, allene, 2-methy-1-buten-3-yne, pentatriene/1-penten-3-yne, 1,3-butadiene, 2-butyne and butatriene, listed in decreasing order of concentration.There was also evidence of the presence of several radical fragments: CH2/CH3, C2H3, C3H3, and C4H5.Quantum yields for each of the products were determined in the photolysis of 2-methyl-1,3-butadiene, performed both in the presence and the absence of additives.Nitric oxide and oxygen were employed as radical scavengers, while hydrogen sulfide and hydrogen iodide were used as radical interceptors.Twelve primary, neutral molecule, reaction channels were proposed and the quantum efficiency assigned for each.The ionization efficiency of 2-methyl-1,3-butadiene was established as n = 0.55 at 10.03 eV.No products formed exclusively via an ion-molecule pathway were identified and therefore the fate of the C5H8+ ion was determined.
