A systematic study of the 213.8-nm (zinc line) photochemistry of 1,3-butadiene has been made either in the absence or in the presence of various additives-such as radical scavengers (02, NO, DI) and collisional quenchers-in the gas phase (pressure between 1 and 500 Torr). The major fate of the photoexcited 1,3-butadiene molecule is isomerization to the 1,2-butadiene structure which may then decompose to methyl and C3H3 radicals ( = 0.64 ± 0.04 at 1 Torr of 1,3-butadiene). Minor processes include decomposition to the acetylene + ethylene couple ( = 0.22 ± 0.02) or to vinylacetylene ( = 0.038 ± 0.003) and molecular hydrogen. These two minor processes occur from different excited states. Some 2-butyne ( < 0.015) is formed by a unimolecular isomerization process. The photolysis of 1,3-butadiene-l,l,4,4-d¡, indicates that at least three different intermediates are involved in the formation of molecular ethylene and acetylene. The C3H3 radicals are not easily intercepted by DI: k(C3H3 + 1,3-butadiene)/A:(C3H3 + DI) = 0.09 ± 0.03. Also at 21 °C and for [DI]/ [ 1,3-butadiene] = 10, the highest ratio used, (3 1 ß + propyne)/^(CH3D) = 0.72 and a fraction of the C3H3 radicals are still not accounted for (reaction with 1,3-butadiene and/or recombination?). The relative energies obtained by ab initio RHF-SCF geometry optimizations for the doublet electronic state of the C3H3 radical structures are £(propargyl) < £(propyn-l-yI) < £(cyclopropen-l-yl) < £(allenyl). General valence bond geometry optimizations and a multiconfigurational self-consistent-field surface scan also show that the propargyl species (1 2B, state) is the lowest energy one. There are probably at least two distinct C3H3 radical structures (different states) present in the far-UV photolysis of 1,3-butadiene.
Devil's club has been used in folk medicine by the native tribes of Alaska and British Columbia for centuries for the treatment of colds, fever, burns, stomach troubles and even tuberculosis.
4,5
ExperimentalStems and roots of O. horridus were collected from the same plant stands on 30 December 2002 near Chilliwack, British Columbia, Canada, at about 200 -300 m altitude. A voucher specimen (no. V219467) was deposited at the Herbarium of the University of British Columbia, Vancouver, Canada. Both oils, the one from the stem and the one from the root, were obtained by steam distillation using a low pressure system with an external steam source. The duration of each distillation was approximately 1 h.The essential oils were analysed by GC on a gas chromatograph Hewlett-Packard 5890 (FID detector) equipped with a polar Supelcowax 10 column and a nonpolar DB-5 column (30 m × 0.25 mm × 0.25 µm). Analyses by GC/MS were performed on a Hewlett-Packard mass spectrometer 5972 at 70 eV coupled to an HP 5890 gas chromatograph using a DB-5 and a Supelcowax 10 column (same as above). The temperature program, used for both GC and GC/MS analyses, was 40°C for 2 min, then 2°C/min to 210°C and held constant for 33 min. The identification of the components was done by comparison of their retention indices with standards and by comparison of their mass spectra with literature values 6 and with our data bank.
Publication costs assisted by Université du Québec a ChicoutimiThe photolysis of cis-2-butene (C2B) was carried out in a static system using nitrogen resonance lines at 7. 10-7.11 eV (174.5-174.3 nm). The main fragmentation processes of the photoexcited (C4H8)** molecule are as follows: C4H8-2** -*• C4H6 -I-2H (H2), = 0.40, and C4H8-2** -* C3H5 + CH3, = 0.38. The energy partitioning between CH3CH=CH and CH3 radicals is discussed. The excited vinylic radicals either decompose yielding acetylene, or isomerize (which is followed by aliene formation), or are stabilized by collisions. The kinetics of the (s-C4H9)* radical decomposition provide some information on the energy distribution of the atomic hydrogen present in the studied system. The stabilization of C4H8-2** molecules and the formation of isomers are inefficient processes between 6.6 and 4 X 104 N m"2 (0.05 and 300 Torr).
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