Radicals dienylic

Reactions of benzophenone-cyclohexa-dienyl radical pair depend on surfactant, magnetic field and l3C content... 

Ultrafast electron diffraction was used to define the structure of the cyclopenta-dienyl radical formed through photodissociation of CpCo(CO)2. The structure obtained reflected the Jahn-Teller distortion from D h symmetry, a dynamic structure thanks to pseudorotations converting dienylic and elongated conformations. ... 

Dole et al. (9, 10, 11, 12) have found by ultraviolet spectroscopy at liquid nitrogen temperature that ultraviolet irradiation of the allylic radicals (II) in polyethylene even give rise to formation of dienylic radicals—i.e., radical III with n = 2. 

Reaction of 711 with terminal alkynes occurs regioselectively living 3-thiahexa-l,5-dienyl radicals 715 which also undergo selective 1,5-ring closure to allylcarbinyl radicals 716. Depending on the substitution pattern, radicals 716 rearrange to cyclopropylcarbinyl radicals 717. From 716 and 717,2,3-dihydrothiophene-3-acetate 718 and 3-thiabicyclo[3.1.0]hexane-6-carboxylates 719 are formed, respectively. 

Aromatic rings are susceptible to OH attack. The oxidation is initiated by addition to the ring, which generates the hydroxycyclohexa-dienyl radical, shown in Eq. (77). For halogenated benzenes, OH- attack at an unsubstituted carbon is preferred. The hydroxycyclohexadienyl radical may disproportionate to produce phenol, shown in Eq. (78). 

Many studies used radiation chemistry to produce the radical and radical cations and anions of various dienes in order to measure their properties. Extensive work was devoted to the radical cation of norbomadiene in order to solve the question whether it is identical with the cation radical of quadricyclane . Desrosiers and Trifunac produced radical cations of 1,4-cyclohexadiene by pulse radiolysis in several solvents and measured by time-resolved fluorescence-detected magnetic resonance the ESR spectra of the cation radical. The cation radical of 1,4-cyclohexadiene was produced by charge transfer from saturated hydrocarbon cations formed by radiolysis of the solvent. In a similar system, the radical cations of 1,3- and 1,4-cyclohexadiene were studied in a zeolite matrix and their isomerization reactions were studied. Dienyl radicals similar to many other kinds of radicals were formed by radiolysis inside an admantane matrix. Korth and coworkers used this method to create cyclooctatrienyl radicals by radiolysis of bicyclo[5.1.0]octa-2,5-diene in admantane-Di6 matrix, or of bromocyclooctatriene in the same matrix. Williams and coworkers irradiated 1,5-hexadiene in CFCI3 matrix to obtain the radical cation which was found to undergo cyclization to the cyclohexene radical cation through the intermediate cyclohexane-1,4-diyl radical cation. 

At intermediate temperatures, vinyl, allyl, methyl-allyl (aC4H7), cyclopenta-dienyl radicals as well as cyclopentadiene are involved in a relevant subset of addition reactions (Faravelli et al., 1998). Vinyl addition to ethylene, through the intermediate pC4H7 and aC4H7 radicals, easily forms butadiene. 

Indoles are the main products from the cyclisation of 2,6-dimethylphenyl-1,4-diazabuta-1,3-dienyl radicals (228), and quinoxalines (229,230) are formed in small amounts (Scheme 54). 

Fig. 6. (/>-(Tri(luoromethyl)phenyl)tetraphenylcyclopenta- Fig. 7. 1-Hydroxycyclohexadienyl radical. H(l) coupling dienyl radicals. H and F hfs constants vs. temperature constant vs. basicity (H = 14.0 + log(y[OH"]) [85Tanl]. [84Kiel]. The numbers in parentheses refer to the molecular Full circles taking y as given by Eq. 2 (see [8STanl]) open...

The oxidation of alkanes, alkenes and simple aromatics at 293 K under NOx rich tropospheric conditions has been studied using laser pulse initiation combined with cw laser long path absorption/LIF for the detection of OH and NO2. In the case of aliphatic hydrocarbons the absolute yield and the kinetics of the formation of these products have been found to be sensitive indicators for the reaction behaviour of the oxy radicals RO. In combination with mechanistic simulations rate constants for individual reactions as well as branching ratios have been derived, which permit the evaluation of the compound specific NO/NO2 conversion factors (NOCON - factors) for the first oxidation steps. In the case of benzene and toluene oxidation the results indicate that reaction of the primary formed X cyclohexa-dienyl radical (X = Cl, OH) with O2 is the dominant pathway, although the rate coefficients were found to be lower than 2 x 10" cmVs. 

D JL Thermal rearrangement of[2-D]bicyclo[3.2.0]-hepta-2,6-dienyl radical 6H 0.400 89Susl... 

Fig. 3. (a) The ESR spectra obtained upon UV irradiation of aqueous H2O2 in the presence of p-toluene sulfonic acid at pH 0.4 (al, identified as the benzyl radical), pH 4.8 (a2, cyclohexa-dienyl radical), and pH 11.5 (a3, a superposition of spectra from three phenoxyl type radicals). Note the different scales. Arrows marked d, t, and q indicate doublet, triplef and quartet spUtt-tings, respectively. The corresponding radical structures are shown in (b). The pH dependence of total signal amplitudes (obtained by integration of an isolated line and then scaled to represent the entire spectrum) are given in (c) for the benzyl radical ( ), the cyclohexadienyl radical (O), and the sum of the three phenoxyl radicals (A). (From Ref. 37 with permission.)... 

The complexation of unsaturated hydrocarbons by transition metals is a powerful activation method that plays a fundamental role in their stoichiometric and catalytic transformation. The bonds formed are governed by jt backbonding. Olefins, dienes and arenes are usually 2-electron L, 4-electron L2, and 6-electron L3 ligands respectively, and alkynes are 2-electron L or 4-electron L2 depending on the needs of the metal. The odd-electron ligands are the 3-electron LX allyl radical and 5-electron L2X dienyl radicals. Cyclopentadienyl and arene sandwich complexes will be examined in Chap. 11. 

Fe-OOH is first formed and abstracts hydrogen from substrate to give a dienyl radical. An autoxidation process is subsequently assumed in Scheme 14. 

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