Benzene Radical Research Articles

Kinetics of the reversible recombination of substituted 2-(p-dimethylaminophenyl)indane-1,3-dion-2-yl radicals

1. We established linear relationships between Δ log 2k−1, Δ log 2k1, and Σσ of the Gammet constants with a positive ρ value, equal to 0.32 and 1.20, respectively. 2. We determined the kinetic and thermodynamic parameters of the recombination reaction of radicals and of the dissociation of dimers in the 2-arylindanedione-1,3 series. 3. The recombination rate constant of 2-arylindane-1,3-dion-2-yl radicals in benzene is activational. In the binary benzene-MO mixture at η≥2sP, the recombination rate constant is fully limited by molecular mobility. In the case of recombination of 5-iodo-2-(p-dimethylaminophenyl) indane-1,3-dion-2-yl radicals, we found that 2k−1 ∼ η−0.5.

Thermodynamic parameters of free radical-dimer equilibria in phenylindandione derivatives

Measurements of the thermodynamic parameters of the free radical-dimer equilibrium in benzene for 2,2′-bis[R-2-(p-dimethylaminophenyl)indan-1,3-diones] with different substituants R on the phthaloyl ring have been carried out. The equilibrium constants satisfy the Hammett equation (p=0.87, benzene, 20‡C). The bond breaking energy of the central C2−C2' bond in the dimers amounts to ∼18–20 kcal/mole The extinction coefficients of the 2-aryl-indan-1,3-dione-2-yl radicals in benzene have been determined. The long-wave band of the radicals displays thermo- and solvatochromism.

An ESR investigation of the structure and rearrangement of the hexamethyl(Dewar benzene) radical cation

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAn ESR investigation of the structure and rearrangement of the hexamethyl(Dewar benzene) radical cationChristopher J. RhodesCite this: J. Am. Chem. Soc. 1988, 110, 13, 4446–4447Publication Date (Print):June 1, 1988Publication History Published online1 May 2002Published inissue 1 June 1988https://doi.org/10.1021/ja00221a073RIGHTS & PERMISSIONSArticle Views74Altmetric-Citations18LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (255 KB) Get e-Alerts Get e-Alerts

Specific solvation effects on electron transfer

This article focuses on the effects of specific solvation on electron transfer (ET) reactions and illustrates how differing configurations of solvent molecules can change the ET rate. The evolution of the ET system is given by a recently developed dynamical model for ET [1]. The dynamical model allows for evolution of the ET system dynamically coupled to the outer solvent and the intramolecular degrees of freedom. The evolution of the ET system is followed in direct time using time-dependent statistical density operators. The initial state of the ET system is selected by a variational scheme, thereby determining an appropriate time-dependent statistical density operator for the initial state. The electronic subsystem is treated by a full ab-initio electronic Hamiltonian and allows for a detailed description of the electronic structure. The ET system consists of a donor, an acceptor, and a selection of solvent/bridge molecules; this encounter is surrounded by a dielectric medium [1, 2]. The actual calculations concern an ET system consisting of benzene anion radical as donor, benzene as acceptor, and three water molecules in the first solvation shell. These calculations show how important specific solvation of the donor-acceptor complex is for the ET process. The ET probability can be increased or decreased depending on the configuration of the water molecules.

Computations of ESR coupling constants in organic radicals. I. General theory and applications to benzene and toluene

We discuss the removal of spin contamination from an unrestricted Hartree-Fock wavefunction and we use the theoretical expressions to calculate the ESR coupling constants of the benzene and toluene radicals and radical anions. We investigate the Jahn-Teller distortion in the benzene radical anion and the rotational motion of the methyl group in the toluene radical anion in order to study their effects on the corresponding ESR spectra. We also present some general predictions regarding the spin and the energy derived from unrestricted Hartree-Fock computations.

ChemInform Abstract: Mass Spectrometry for Investigations of Gas‐Phase Radical Cation Chemistry. The Two Step Cycloaddition of the Benzene Radical Cation and 1,3‐Butadiene.

Abstract Mass spectrometric techniques are now used extensively for the study of gas-phase radical cation chemistry. The generation and structural properties, the unimolecular and bimolecular chemistry of some representative radical cation systems, and the methods of study are reviewed. The structure of the ionmolecule adduct produced in the reaction of the benzene radical cation and neutral 1,3-butadiene was investigated by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition spectrum. The CAD spectrum of the adduct changes dramatically as a function of the degree of collisional stabilization. This observation is interpreted in terms of two distinct structures for the adduct. The species that is stabilized at 0.7 Torr has a CAD spectrum similar to the 2-phenyl-2-butene radical cation. The second structure, stabilized at 0.1 Torr, has a CAD similar to that of 1-methylindan. The results of these experiments are interpreted in terms of a two-step cycloaddition mechanism for the formation of the 1-methylindan radical cation.

Electron transfer reactions dynamically coupled to a dielectric medium: Orientational effects and bridge assistance

A new treatment for studying electron transfer reactions is considered. The treatment allows for a detailed description of the electronic structure and is therefore appropriate for a complete description of weakly interacting electron transfer reactions. The initial state for the electron transfer system is selected by a variational scheme. The electron transfer is pictured to take place in an encounter complex consisting of the donor, the acceptor, and (optionally) a solvent/bridge molecule. The electronic structure of the encounter complex is dynamically coupled to the surrounding solvent, and the direct time evolution of the electron transfer system is followed by a nonlinear time-dependent Hartree-Fock method. We present examples with benzeneanion radical as the donor, pyridine as the acceptor, and water as the bridge/solvent molecule. The general formalism appears to be a useful approach for studying electron transfer reactions in solution.

Pyrolysis of benzenethiol

Flow pyrolysis of benzenethiol at 700 °C or vacuum pyrolysis of benzenethiol at 800 °C yields benzene, diphenyl sulphide and diphenyl disulphide as the major products. Dibenzothiophene, biphenyl, thianthrene and diphenyl trisulphide are minor products. Co-pyrolysis of benzene-d 6 and natural isotopic abundance benzenethiol yields deuterated and non-deuterated products, indicating that the product-forming sequence is initiated by phenyl radical formation. The phenyl radicals abstract hydrogen atoms from benzenethiol to yield benzene and phenylthio radicals. Coupling of phenylthio radicals yields diphenyl disulphide. Diphenyl sulphide and the minor products are diphenyl disulphide pyrolysis products.

ChemInform Abstract: The High‐Temperature Oxidation of Aromatic Hydrocarbons

Chemical mechanisms of the atmospheric pressure, high-temperature (875-1500 K) gas-phase oxidation of benzene, toluene, ethylbenzene, and propylbenzene are described and discussed. Oxidation trends evident from turbulent flow reactor experiments serve as the basis for the mechanisms of the oxidation of benzene and alkylated aromatics. The potential effects of very high temperatures and pressures on the chemistry of oxidation of aromatics are described. The oxidation of benzene and phenyl radical has been found to proceed in a stepwise C6-C5-C4 sequence. Species profiles obtained from flow-reactor experiments suggest that the oxidation of benzene and phenyl radical follows the generalized route via phenoxy, cyclopentadienyl and butadienyl radical. The oxidation of the C4 species branches into multiple pathways that yield copious amounts of ethylene and acetylene. Certain major trends are evident: the alkylated aromatics on initial attack either form styrene, benzyl radical or benzene. The styrene reacts further to produce a benzyl radical or benzene. The oxidation of an alkylated aromatic hydrocarbon appears eventually to reduce to the oxidation of either phenyl radical or benzene.

Stopped-Flow Investigation of Antioxidant Activity of Tocopherols

Abstract It was observed by ESR measurement that the oxidation of α-, β-, γ-, and δ-tocopherols (vitamin E) with a stable phenoxyl radical in benzene immediately gives corresponding tocopheroxyl radicals. The rates of reaction of α-, β-, γ-, and δ-tocopherols with the stable phenoxyl radical in ethanol solution have been determined spectrophotometrically using stopped-flow technique, as a model reaction of tocopherols with unstable free radicals (ROO·, RO·, and HO·) in biological systems. The second-order rate constants obtained are (5.12±0.36)×103 (α-Toc), (2.24±0.04)×103 (β-Toc), (2.42±0.16)×103 (γ-Toc), and (0.51±0.01)×103 (δ-Toc), M−1 s−1 in ethanol at 25.0 °C. The relative rates agree well with those obtained from studies of the reactivities of tocopherols toward poly(styrylperoxyl) and galvinoxyl radicals by O2 consumption and by ESR method, respectively. The results suggest that the relative reactivities, that is, relative antioxidant activities of tocopherols do not depend on the kinds of unstable free radicals reacted.

Formation of radicals and catalytic activity of H-ZSM-5-type zeolites in unsaturated hydrocarbon conversions: Part 2. Radical formation upon adsorption of aromatic compounds

The formation of cation radicals upon adsorption of different aromatic compounds at 20–250 °C on H-ZSM-5 zeolites has been studied. It is shown that the concentration of the strong radical-forming sites in H-ZSM-5 (per Al 3+ ion of lattice) is not lower than that in H-mordenite. The selective blocking of external sites by 2,4,6-trimethylpyridine does not prevent the formation of benzene or p-xylene radicals, i.e. the majority of aromatic radicals formed are located inside the H-ZSM-5 channels. In the case of large molecules, some peculiarities of radical formation due to steric hindrance have been observed. The role of chemisorbed oxygen in the processes of aromatic cation radical formation on H-ZSM-5 and H-mordenite is discussed.

The high-temperature oxidation of aromatic hydrocarbons

Chemical mechanisms of the atmospheric pressure, high-temperature (875–1500K) gas-phase oxidation of benzene, toluene, ethylbenzene and propylbenzene are described and discussed in detail. Major oxidation trends evident from turbulent flow reactor experiments serve as the basis for the overall mechanisms of the oxidation of benzene and alkylated aromatics which are also presented. The potential effects of very high temperatures and pressures on the chemistry of oxidation of aromatics are described. The oxidation of benzene and phenyl radical has been found to proceed in a stepwise C 1C 5C 4 sequence. Species profiles obtained from flow-reactor experiments suggest that the oxidation of benzene and phenyl radical follows the generalized route-phenoxy, cyclopentadienyl and butadienyl radical. The oxidation of the C 4 species branches into multiple pathways that yield copious amounts of ethylene and acetylene. The alkylated aromatics are oxidized through a large number of reaction pathways. However, certain major trends are evident: the alkylated aromatics on initial attack either form styrene, benzyl radical or benzene. The styrene reacts further to produce a benzyl radical or benzene.In general, the oxidation of an alkalated aromatic hydrocarbon appears eventually to reduce to the oxidation of either phenyl radical or benzene.

Mass spectrometry for investigations of gas-phase radical cation chemistry : The two step cycloaddition of the benzene radical cation and 1,3-butadiene

Mass spectrometric techniques are now used extensively for the study of gas-phase radical cation chemistry. The generation and structural properties, the unimolecular and bimolecular chemistry of some representative radical cation systems, and the methods of study are reviewed. The structure of the ionmolecule adduct produced in the reaction of the benzene radical cation and neutral 1,3-butadiene was investigated by collisionally stabilizing the adduct and then acquiring its collision-activated decomposition spectrum. The CAD spectrum of the adduct changes dramatically as a function of the degree of collisional stabilization. This observation is interpreted in terms of two distinct structures for the adduct. The species that is stabilized at 0.7 Torr has a CAD spectrum similar to the 2-phenyl-2-butene radical cation. The second structure, stabilized at 0.1 Torr, has a CAD similar to that of 1-methylindan. The results of these experiments are interpreted in terms of a two-step cycloaddition mechanism for the formation of the 1-methylindan radical cation.

Spin trapping of radicals in tritiated benzene

Decay of tritium in labelled benzene, containing PBN or ND as spin traps, produced nitroxides, the ESR spectra of which established phenyl as the sole radical. The yield of the PBN-Ph adduct was compared with that obtained when tritiated methanol was dissolved in non-radioactive benzene. These experiments demonstrated that about 75% of radicals arise due to internal·β radiolysis with a G value of about 0.05, indicating a lack of any significant LET effect as compared with hard γ rays.

Comparative hammett studies of imidoyl, benzylic, aldehydic hydrogens transfer and related reaction by [formula omitted]-butoxyl radical

The polar transition states involved in the hydrogen transfer reactions of N-benzylideneanilines, toluenes, benzaldehydes, and anisoles by t -butoxyl radical in benzene at 130°C have been comparatively discussed in terms of the values of the ρ and the k a o/k d.

E.s.r. spectroscopic investigations on tight ion pairs in the lithium salt of the benzene radical anion

The occurrence of resolved splittings due to the 7Li nucleus in the e.s.r. spectrum of the lithium salt of the benzene radical anion in 2-methyltetrahydrofuran (MTHF) provides fundamental information about the ion pair structure and a rationalization of the e.s.r. line broadening effects.

ChemInform Abstract: ALKYL AND SILYL DERIVATIVES OF BENZENE RADICAL CATIONS FORMED BY RADIOLYSIS: AN ELECTRON SPIN RESONANCE STUDY

Chemischer InformationsdienstVolume 15, Issue 41 Physical Organic Chemistry ChemInform Abstract: ALKYL AND SILYL DERIVATIVES OF BENZENE RADICAL CATIONS FORMED BY RADIOLYSIS: AN ELECTRON SPIN RESONANCE STUDY D. N. R. RAO, D. N. R. RAOSearch for more papers by this authorH. CHANDRA, H. CHANDRASearch for more papers by this authorM. C. R. SYMONS, M. C. R. SYMONSSearch for more papers by this author D. N. R. RAO, D. N. R. RAOSearch for more papers by this authorH. CHANDRA, H. CHANDRASearch for more papers by this authorM. C. R. SYMONS, M. C. R. SYMONSSearch for more papers by this author First published: October 9, 1984 https://doi.org/10.1002/chin.198441076AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue41October 9, 1984 RelatedInformation

ChemInform Abstract: MEASUREMENT OF THE DIPOLE MOMENT OF A PEROXYL RADICAL BY MICROWAVE DIELECTRIC ABSORPTION

The technique of time-resolved microwave dielectric absorption has been used to measure the dipole moment of the benzylperoxyl radical in benzene, cyclohexane, and decane solutions. The radicals were produced by photolysis of dibenzyl ketone in oxygen-containing solutions with pulses of light at 280 nm from a frequency-doubled dye laser. Benzyl chloride and cyanide were used to model the rotational relaxation behavior of the radical. A dipole moment of 2.4 +/- 0.2 D was found. It is suggested that this polarity may be large enough to significantly affect the location of the portion of the molecule bearing the peroxyl group in radicals formed in heterogeneous systems as micelles or bilayers in water. 16 references, 1 figure, 4 tables.

Measurement of the dipole moment of a peroxyl radical by microwave dielectric absorption

The technique of time-resolved microwave dielectric absorption has been used to measure the dipole moment of the benzylperoxyl radical in benzene, cyclohexane, and decane solutions. The radicals were produced by photolysis of dibenzyl ketone in oxygen-containing solutions with pulses of light at 280 nm from a frequency-doubled dye laser. Benzyl chloride and cyanide were used to model the rotational relaxation behavior of the radical. A dipole moment of 2.4 +/- 0.2 D was found. It is suggested that this polarity may be large enough to significantly affect the location of the portion of the molecule bearing the peroxyl group in radicals formed in heterogeneous systems as micelles or bilayers in water. 16 references, 1 figure, 4 tables.

Geometrical and electronic structure of fluoro-substituted benzene radical anions based on quantum chemical analysis of hyperfine interactions

Abstract The INDO method has been employed to calculate the isotropic and anisotropic hyperfine interactions for some geometrical structures of the C 6 F 6 − , C 6 HF 5 − , 1,2,4,5-F 4 C 6 H 2 − radical anions. The π and σ states of planar radical anions have been considered together with three types of non-planar structures: (a) with out-of-plane distortions of the benzene ring following the “chair” pattern: (b) with neighbouring fluorine atoms displaced in opposite directions from the ring plane due to their electrostatic repulsion: (c) with symmetric (of type) displacement of CF bonds due to the interaction between the ground and lowest excited σ-electron states within the pseudo-Jahn-Teller effect. It is the last model that describes all experimental data on magnetic resonance parameters. This model is also preferable for energy reasons. Most likely, this type of non-planar structures reflects the basic features of the real geometry of the above radical anions whose ground state may be termed as pseudo-π-electronic since the unpaired electron occupies an orbital that is a linear combination of the π and σ orbitals of the corresponding planar structure with a prevailing π component.