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Showing papers on "Homolysis published in 1984"


Journal ArticleDOI
01 Apr 1984-Lipids
TL;DR: Treatment of isomeric methyl linoleate hydroperoxides with a Lewis acid, BF3, in anhydrous ether led to a carbon-to-oxygen rearrangement that caused cleavage into shorter-chain aldehydes, which resembled the one catalyzed by the plant enzyme, hydroperoxide lyase.
Abstract: Treatment of isomeric methyl linoleate hydroperoxides with a Lewis acid, BF3, in anhydrous ether led to a carbon-to-oxygen rearrangement that caused cleavage into shorter-chain aldehydes. Methyl (9Z,11E)-13-hydroperoxy-9,11-octadecadienoate afforded mainly hexanal and methyl (E)-12-oxo-10-dodecenoate, whereas methyl (10E,12Z)-9-hydroperoxy-10,12-octadecadienoate cleaved into 2-nonenal and methyl 9-oxononanoate. The 2 aldehydes obtained from each hydroperoxide isomer were uncharacteristic of the complex volatile profile usually obtained by β-scission of oxy radicals derived from homolysis of the hydroperoxide group. Rather, the reaction resembled the one catalyzed by the plant enzyme, hydroperoxide lyase.

83 citations


Journal ArticleDOI
01 Oct 1984-Lipids
TL;DR: In this paper, the genesis of volatile lipid oxidation products, thermal homolytic and acid heterolytic decomposition processes were compared, and no dialdehydes were identified under their thermal decomposition conditions.
Abstract: To elucidate the genesis of volatile lipid oxidation products, thermal homolytic and acid heterolytic decomposition processes were compared. Secondary oxidation products were decomposed thermally (200 C), and the volatiles formed were identified by capillary gas chromatography-mass spectrometry (GC-MS). Oxidation products also were decomposed in the presence of HCl-methanol, and the resulting dimethyl acetals were identified by GC-MS. The volatile thermal decomposition products were those expected by homolytic β-scission on both sides of the hydroperoxide group. No dialdehydes were identified under our thermal decomposition conditions. In contrast, the acetals formed by acid decomposition were those expected by selective heterolytic scission between the hydroperoxide group and the allylic double bond. Dialdehydes identified from acid decomposition of cyclic peroxides and dihydroperoxides included malonaldehyde and 2,4-hexadienedial.

72 citations


Journal ArticleDOI
TL;DR: Etude des reactions de CpFe(CO) 2 CX 3 (X=F,Cl,Br) avec les electrophiles donnant des complexes carbene cationiques de type [CpFe[CX 2] + tres sensibles a l'humidite.

58 citations


Journal ArticleDOI
TL;DR: Alkyl thiyl radicals produced by the homolytic decomposition of thionitrites are detected by ESR spin trapping using 5,5-dimethyl-1-Δ-pyrroline-Noxide (DMPO) as mentioned in this paper.

57 citations


Journal ArticleDOI
TL;DR: Etude de la photodissociation d'halogenomethyl-1 and -2 naphtalenes dans lhexane a temperature ambiante par spectroscopie d'emission and d'absorption as discussed by the authors.
Abstract: Etude de la photodissociation d'halogenomethyl-1 et -2 naphtalenes dans l'hexane a temperature ambiante par spectroscopie d'emission et d'absorption. L'excitation a 266 ou 269 nm dans l'etat S 2 (π, π*) conduit a l'homolyse de la liaison C−H. Emission des radicaux naphtyle methyl-1 et -2

52 citations



Journal ArticleDOI
TL;DR: In this article, photoinitiated cationic polymerization by photosensitization of diphenyliodonium and triphenylsulfonium salts is shown to proceed by two distinct electron transfer processes: (1) direct electron transfer from excited-state photosensitizers, and (2) indirect electron transferring from photogenerated radicals.

48 citations


Book ChapterDOI
TL;DR: In this article, the photochemistry of aryl halides and related compounds is discussed, and the exact mechanism for photoinduced homolysis of these compounds is dependent upon both the nature of the halogen substituent and the ayrl group.
Abstract: Publisher Summary This chapter discusses the photochemistry of aryl halides and related compounds. Due to the widespread use of substituted aryl halides as pesticides, electrical insulators, moth proofing agents, etc. and the environmental problems which the use of these compounds pose, it seems worthwhile reconsidering the photochemistry of these compounds. Furthermore, the photoinduced decomposition of aryl halides is used extensively in synthesis, and much of this latter work has been recently reviewed. It is well established that on photolysis, many aryl halides undergo homolysis to generate aryl radicals and halogen atoms. The question as to whether the excited singlet or triplet state or indeed both excited states are responsible for reaction, is of considerable importance. Thus, if reaction occurs from the excited singlet state, the homolytic process may well be in competition with an electrocyclic reaction. The precise mechanism for photoinduced homolysis of aryl-halogen compounds is dependent upon both the nature of the halogen substituent and the aryl group.

47 citations


Journal ArticleDOI
TL;DR: In this paper, the transient absorption phenomena and quantitative estimates of electron-transfer-mediated yields have been examined by 337.1 nm laser flash photolysis for photoproduction of substrate radicals/radical cations and sensitizer triplet as a result of charger-transfer interaction with 1,4-dicyanonaphthalene (DCN) single acceptor.
Abstract: Several organic substrates (donors) known to undergo oxidative C-C bond cleavage upon steady-state irradiation under electron-transfer photosensitization have been examined by 337.1 nm laser flash photolysis for photoproduction of substrate radicals/radical cations and sensitizer triplet as a result of charger-transfer interaction with 1,4-dicyanonaphthalene (DCN) single (acceptor). The transient-absorption phenomena and quantitative estimates of electron-transfer-mediated yields show that for substrates such as 1-(diphenylmethyl)cyclohepta-2,4,6-triene and aryl-substituted pinacols and pinacol-ethers characterized by relatively unstable, short-lived, radical cations, a substantial fraction of arylmethyl radicals are generated fast via back electron transfer in the photogenerated ion pair. In other cases, longer lived radical cations (solvated) that either undergo intramolecular electron transfer leading to C-C bond fragmentation (e.g., with 1,1,2,2-tetraphenylethane) or diffusional back donation of electron from the DCN radical anion (e.g., with p-methoxy- and p-methyl-substituted bibenzyls). Within small groups of closely related quenchers, radical and radical ion yields are found to depend systematically on the structures, chemical nature, and oxidation potentials of the substrates. 18 references, 5 figures, 1 table.

40 citations


Journal ArticleDOI
TL;DR: In this paper, a homolytic monoelectronic α-elimination process was used to obtain Germylenes, R2Ge, germanium-centered radicals, α-digermyl diradicals and digermenes.

33 citations


Journal ArticleDOI
01 May 1984-Fuel
TL;DR: In this paper, the reactions of model compounds containing methylene and ether bridges were examined, in the temperature range 350-400 °C, and the activation energy was relatively independent of these effects.

Journal ArticleDOI
01 Jun 1984-Fuel
TL;DR: In this paper, the authors investigated the influence of coal, phenyl sulphide, 9, 10-anthraquinone, tetracene, phenol and benzoic acid on the rates of decomposition of diphenylalkanes.

Journal ArticleDOI
TL;DR: In this paper, a range of alkyl(pyridine)cobaloximes and related compounds in dilute solutions in methanol or 2-methyltetrahydrofuran at 77 K to 60Co γ-rays resulted in electron capture.
Abstract: Exposure of a range of alkyl(pyridine)cobaloximes and related compounds in dilute solutions in methanol or 2-methyltetrahydrofuran at 77 K to 60Co γ-rays resulted in electron capture. For the methyl derivative the pyridine ligand was lost leaving a novel CoII derivative whose e.s.r. parameters suggests a (dz2)1 configuration (z is normal to the oxime plane). The 13CH3 derivative gave well defined hyperfine coupling 13C in accord with the proposed structure. Other alkyl derivatives gave similar similar results, the pyridine ligand being lost in preference to the alkyl ligand. These results make an interesting contrast with previous results for alkylcobalamins, for which initial elctron addition was into a corrin π* orbital. The chloro derivative lost Cl– in preference to pyridine on electron addition. The chlorotriphenylphosphine derivative gave evidence for electron addition into the dz2 orbital, chloride ions being lost on annealing above 77 K. The hydridotriphenylphosphine derivative lost hydrogen on electron addition: possible mechanisms for this reaction are discussed.On photolysis at 77 K in CD3OD solution poorly defined e.s.r. features for CoII complexes were obtained together with well defined features for the alkyl radicals [·CH3, ·CH2CH3, ·CH(CH3)2 and ·C(CH3)3, the last being formed from (CH3)2CHĊH2 radicals]. At high microwave powers broad features tentatively assigned to CoII···R · pairs were detected, and the marked broadening of the CoII features is also interpreted in terms of such triplet-state pairs. Similar pair trapping was postulated for the photolysis of alkyl cobalamins. These e.s.r. results are compared with the e.s.r. doublet detected when reacting mixtures of substrates and the enzyme–coenzyme B12 are cooled to 77 K. These results suggest that the primary act of photolysis is homolysis of the Co—C bond. This conclusion is discussed in the light of other e.s.r. studies of these systems.


Journal ArticleDOI
TL;DR: Alkyl iodides and benzoyl peroxides provide a new general method of homolytic alkylation of protonated heteroaromatic bases as mentioned in this paper, and the substitution is selective in the positions ortho and para to the heteroatom.

Journal ArticleDOI
TL;DR: In this paper, α-Methylene-γ-butyrolactones were prepared using butoxyallene via stereoselective homolytic carbocyclization of vinyl radicals, similarly, β-methylene analogues were also prepared.
Abstract: α-Methylene-γ-butyrolactones were prepared using butoxyallene via stereoselective homolytic carbocyclization of vinyl radicals, similarly, β-methylene analogues were also prepared.

Journal ArticleDOI
TL;DR: In this paper, the results were interpreted in terms of a photosubstitution reaction from the singlet state, which involves electrophilic attack to the solvent by a very reactive intermediate.

Journal ArticleDOI
TL;DR: In this paper, the homolytic methylation of pyrimidine in aqueous solution has been investigated with three different radical sources: ButOOH-Fe2+, MeCO2H-S2O82––Ag+, and MeSOMe-H2O2−Fe2+.
Abstract: The homolytic methylation of pyrimidine in aqueous solution has been investigated with three different radical sources: ButOOH–Fe2+, MeCO2H–S2O82––Ag+, and MeSOMe–H2O2–Fe2+. This last reagent, used for the first time in homolytic aromatic substitution, turned out to be the most efficient. The orientation of mono-and poly-methylated derivatives is discussed on the basis of polar effects.


Journal ArticleDOI
TL;DR: In this article, two novel organocobalt(III) complexes containing a σ-bonded alkyl group (R), a mixed tridentate ligand and either a chelating diamine or two monodentate Lewis bases were synthesized.

Journal ArticleDOI
TL;DR: In this paper, N-benzoylaziridines with strong electron sources were used for the formation of ketyls and radicals, both of which are postulated intermediates in the single electron transfer mechanism of nucleophilic ring opening of activated aziridine.
Abstract: Reactions of N-benzoylaziridines with strong electron sources provided direct evidence for the formation of ketyls (2) and radicals (3), both of which are postulated intermediates in the single electron transfer mechanism of nucleophilic ring opening of activated aziridines.

Journal ArticleDOI
TL;DR: In this article, the electron spin resonance (ESR) spectra observed after the addition of TCNB to polystyrene (PSt) in benzene solution were assigned to the nitroxide radicals (spin adducts) of the PSt radicals,, and were deduced from comparisons between observed and computer simulated spectra.

Journal ArticleDOI
TL;DR: The range of isomer distribution found within the reaction of each arene with bromine is consistent with two competing processes involved in the formation of the aryl bromides; one of these might be the direct homolytic substitution by Bromine atoms upon the arene as discussed by the authors.
Abstract: Photochemical bromination of benzene, fluorobenzene, chlorobenzene, t-butylbenzene, α,α,α-trifluorotoluene, and (in tetrachloromethane) biphenyl and naphthalene gives substitution products and adducts such as 1,2,3,4,5,6-hexabromocyclohexane (1). The decomposition of (1) and of the analogous chlorobenzene adduct (3) under photochemical conditions gives the parent arene, the mono-brominated halogenobenzene, and bromine which may be scavenged by toluene to give benzyl bromide or by benzene to give bromobenzene and dibromobenzenes. Addition is a kinetically controlled process, so that the mechanism of formation of these aryl bromides must be largely through the reversible formation of these adducts. This is consistent with the unusual orientation of apparent attack by bromine upon the arene substrates, since the relative amounts of the isomeric aryl bromides is a consequence of the relative stabilities and ease of elimination of HBr and Br2 from a family of adducts.The range of isomer distribution found within the reaction of each arene with bromine is consistent with two competing processes involved in the formation of the aryl bromides; one of these might be the, direct homolytic substitution by bromine atoms upon the arene.

Journal ArticleDOI
TL;DR: The case in which a stable radical is formed as a result of elimination constitutes an exception as discussed by the authors, where the acceptors contributing to radical elimination are atoms of metals, organometallic and organic radicals, and neutral molecules.
Abstract: 1. Disappearance of the free valence in organometallic derivatives of o-semiquniones with IVB group metals linked with elimination of one of the radicals on the IVB group element, proceeds by a bimolecular mechanism with participation of an external acceptor of the radical. The case in which a stable radical is formed as a result of elimination constitutes an exception. 2. Examples of acceptors contributing to radical elimination are atoms of metals, organometallic and organic radicals, and neutral molecules.

Journal ArticleDOI
TL;DR: In this article, a photolysis of [M(CO)5M′ (CO)3(dab)] (M, M′ = Mn, Re; dab = 1,4-diazabuta-1,3-diene, RN, RNCHCH-NR) in 2-Me-THF leads to both homolytic and heterolytic splitting of the metal bond depending on the solution temperature.

Journal ArticleDOI
TL;DR: In this paper, a reaction scheme was proposed which included homolytic TeTe bond cleavage to produce RTe radicals and a subsequent chain reaction involving alcohol, and the observed rate constant is independent of temperature, within experimental error.

Journal ArticleDOI
TL;DR: Deuterium isotopic labeling shows that the rate increase is accompanied by a change from an intramolecular to a radical mechanism involving the abstraction of hydrogen by the methyl groups as discussed by the authors.

Journal ArticleDOI
TL;DR: The photostationary state reached on irradiation (313 nm) is rich in the trans isomer (the ratio cis : trans is 27 : 73 in cyclohexane), because of the higher absorption coefficient of the cis isomer at this wavelength as discussed by the authors.
Abstract: Upon direct u.v. irradiation in cyclohexane, benzene, alcohol, or chloroform solution, [Sn(CPhCHPh)Me3](1) undergoes cis-trans isomerization about the olefin double bond as the only efficient reaction. No evidence has been found for either homolytic or heterolytic photocleavage of the Sn–C bond as a primary process. Unusually for stilbenes the photostationary state reached on irradiation (313 nm) is rich in the trans isomer (the ratio cis : trans is 27 : 73 in cyclohexane), because of the higher absorption coefficient of the cis isomer at this wavelength. Isomerization may also be induced following energy transfer from organic sensitizers. Similar results have been observed for [Sn(CPhCMePh)Me3](2).

Journal ArticleDOI
TL;DR: Cyclic voltammetry and controlled-potential electrolysis of the disulphone (1a) in dimethyl sulphoxide show that its transformation into the dibenzothiophene dioxide (2a), in the presence of a base, is an efficient electrocatalytic process as discussed by the authors.
Abstract: Cyclic voltammetry and controlled-potential electrolysis of the disulphone (1a) in dimethyl sulphoxide show that its transformation into the dibenzothiophene dioxide (2a), in the presence of a base, is an efficient electrocatalytic process.