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1988 (1)
1Author    Xian-Ming Pan, Eugenie Bastian, Clemens Von SonntagRequires cookie*
 Title    The Reactions of Hydroxyl Radicals with 1,4-and 1,3-Cyclohexadiene in Aqueous Solution A Pulse Radiolysis and Product Study  
 Abstract    The reactions of radiolytically generated hydroxyl radicals and H atoms with 1,4-and 1,3-cyclohexadiene were studied by pulse radiolysis and product analysis. Hydrogen abstraction from these substrates by the OH radical yields the cyclohexadienyl radical (f (310 nm) = 4400 dm 1 mol" 1 cm"' from the reaction of the H atom with benzene) with an efficiency of 50% (0.29 ,«moI /"') in the case of 1,4-cyclohexadiene and 25% (0.15,«mol /"') in the case of 1,3-cyclohexadiene as determined by pulse radiolysis. The remaining OH radicals add to the olefin. In 1,4-cyclohexa-diene the yield of the resulting adduct radicals has been determined in a steady-state "'Co-y-irradiation experiment by reducing it with added 1,4-dithiothreitol (DTT) to 4-hydroxycyc-lohexene. There are two sites of OH radical attack in the case of 1,3-cyclohexadiene, and only the alkyl radical is reduced quantitatively by DTT (G(3-hydroxycyclohexene) = 0.15 ,«mol J '). From material balance considerations it is concluded that the allylic radical must be formed with a G value of 0.28 «mol J~ x but largely escapes reduction by DTT (G(4-hydroxycyclohexene) = 0.03 ,«mol y 1). H atoms add preferentially to the double bonds of 1,4-and 1,3-cyclohexadiene (78% and 93%, respectively), while the O t radical (the basic form of the OH radical) undergoes mainly H-abstraction (92% and 83%. respectively). The radicals formed in these systems decay bimolecularly (2k = 2.8xl0 4 dm' mop 1 s~'). In their combination reactions the cyclohexadienyl radicals form the four possible dimers in propor-tions such that the dienyl radical moiety shows a 2:1 preference to react from its central (la) rather than from a terminal carbon atom (lb). Cyclohexadienyl radicals and the OH-and H-adduct radicals also cross-terminate by disproportionation and dimerization. Material balance has been obtained for the 1,4-cyclohexadiene system in N : 0-saturated solution (10 : mol dm 3) at a dose rate of 0.14 Gy s" 1 , the products (G values in «mol J ') being: benzene (0.085), 4-hydroxycyclohexene (0.25), cyclohexadienyl-dimers (0.144), cyclohexadienyl-OH-adduct-dimers (0.02), OH-adduct-dimers (0.02). Some of the 4-hydroxycyclohexene is formed in an H-abstraction reaction by the OH-adduct radical from 1,4-cyclohexadiene. 
  Reference    Z. Naturforsch. 43b, 1201—1205 (1988); received April 13 1988 
  Published    1988 
  Keywords    1, 4-Cyclohexadiene, 1, 3-Cyclohexadiene Hydroxyl Radical, Cyclohexadienyl Radical, Pulse Radiolysis 
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 TEI-XML for    default:Reihe_B/43/ZNB-1988-43b-1201.pdf 
 Identifier    ZNB-1988-43b-1201 
 Volume    43