Cyclopentadienyl Radical Research Articles

Rotationally resolved electronic spectrum of jet-cooled deuterated cyclopentadienyl radical

The completely rotationally resolved laser-induced fluorescence spectrum of the perdeutero cyclopentadienyl radical, C 5D 5, is obtained in a supersonic free jet expansion. Combination of the rotational constants of C 5D 5 with those previously obtained for C 5D 5 allow the determination of the r 0 structure. A discussion of the radical's geometry is based upon this structure as well as the observed nuclear spin statistics, the inertial defect, and the Jahn-Teller distortion parameters.

Thermal Decomposition of Phenyl Alkyl Ethers

AbstractReaction products and intermediates of the thermal conversions (temperature range: 600 to 1200°C, total pressure about 120 mPa) of phenyl methyl ether (1), phenyl ethyl ether (2), and m‐cresyl methyl ether (3) were determined in a pyrolysis apparatur set combined with mass spectral „real time”︁ analysis. In all cases, the predominant initial process was PhO–R bond homolysis. Phenoxy type radicals thus generated decompose unimolecularly to cyclopentadienyl type radicals and carbon monoxide. In runs with 1 and 2 cyclopentadienyl dimers (C10H10) were formed and, in addition, at temperatures >1000°C, naphthalene (C10H8). Under similar conditions the m‐methylphenoxy radical (from 3) suffers CO elimination providing the methylcyclopentadienyl radical which chiefly gives benzene instead of the dimers or the products derived from it. Under the applied conditions only bimolecular stabilization of the unsubstituted cyclopentadienyl radical proved possible, whereas the methyl substituted radical has a chance for unimolecular stabilization, too, as a result of which fulvene is formed through the loss of hydrogen. Fulvene is a direct benzene precursor.

Benzene oxidation perturbed by NO2 addition

By altering the O, H and OH radical concentrations through the addition of NO2 to benzene oxidation studies in a flow reactor, it has been shown that the predominate route to the formation of the important intermediate phenoxy radical is by the reaction of phenyl with O2. These studies have also shown that O atom addition to benzene to form phenol which then reacts with radicals is not an important route to the formation of phenoxy. Further, the fate of the cyclopentadienyl radical, another important intermediate, has been shown to be determined not by reactions with O2, but with members of the OH, H and O radical pool.

Rotationally resolved electronic spectrum of jet-cooled cyclopentadienyl radical

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRotationally resolved electronic spectrum of jet-cooled cyclopentadienyl radicalLian Yu, Stephen C. Foster, James M. Williamson, Michael C. Heaven, and Terry A. MillerCite this: J. Phys. Chem. 1988, 92, 15, 4263–4266Publication Date (Print):July 1, 1988Publication History Published online1 May 2002Published inissue 1 July 1988https://doi.org/10.1021/j100326a004RIGHTS & PERMISSIONSArticle Views230Altmetric-Citations54LEARN 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 (519 KB) Get e-Alerts

Synthesis, characterization and mass spectra of the titanocene derivatives Cp 2Ti(XC 6F 5) 2 (X=O, S)

Two different methods of preparation and the 1H NMR and mass spectra of the titanocene complexes, Cp 2Ti(XC 6F 5) 2 (X=O, S; Cp=η 5-C 5H 5), are discussed. The mass spectra indicate a loss of cyclopentadienyl and pentafluorophenylchalcogeno radicals and, in the case of the thiolate derivative, a rearrangement to Cp 2TiF 2. Overmore, neutral particle eliminations of HF and CpH are observed. The ion genesis of the phenolate complex was proven by persecution of metastable transitions using the linked scan technique. The 1H NMR chemical shffts are interpreted in terms of electronegativity and donor ability of the coordinated chalcogen atoms.

ChemInform Abstract: Acyclic Pentadienyl Metal Complexes

Publisher Summary This chapter reviews the chemistry of complexes formed by the related acyclic pentadienyl group. η 1 -cyclopentadienyl groups are found both in main group derivatives and in transition metal complexes. The electron affinities of the pentadienyl and cyclopentadienyl radicals in the gas phase are 87 and 173 kJ mol –1 and the first ionization energies 752 and 839 kJ mol –1 , respectively. The metal can be bonded η 3 , which is usually favored for lithium or η 5 , which is adopted by the larger potassium ion. 13 C-nuclear magnetic resonance (NMR) spectra show that the negative charge in the pentadienylmetal derivatives of groups I, II, and III resides preferentially at the terminal and central positions. Allyl silanes and stannanes are established as useful reagents in organic synthesis. Electrophilic attack occurs at the terminal carbon atom of the allyl system, leading to allylic transposition in the product. The first binary pentadienyl complex of a transition element, bis (pentadienyl)-chromium, was obtained from PlNa and CrCl 2 . Pentadienyltricarbonyliron cations are readily attacked by nucleophiles. They are more reactive in this respect than the corresponding cyclic complexes. Cyclopentadienyltricarbonylmanganese (cymantrene) is extensively investigated. Typical reactions include photochemical substitution of carbonyl groups by other ligands and the electrophilic substitution of the cyclopentadienyl ring. Some unusual complexes that include pentadienyl or related ligands have been obtained from the reactions of alkynes with various transition-metal complexes.

Experimentelle und theoretische Untersuchungen an Kohlenwasserstoffen der Formel C5H6: Pyrolyse von Cyclopenta‐1,3‐dien

Experimental and Theoretical Investigations on Hydrocarbons of the Formula C5H6: Pyrolysis of 1,3‐CyclopentadieneThe details of high temperature chemistry of the conversion of 1,3‐cyclopentadiene (CPD) are unknown. Therefore the pyrolysis of CPD was studied under various reaction conditions in labscale dimension. The attempt to interpret the composition of the reaction products only on the basis of convenient axiomes does not seem satisfactory. For that reason heats of formation and relative stabilities for 25 closed and open shell hydrocarbons of the formula C5H6 were calculated using the MINDO/3 procedure. These enthalpy values were used to estimate heats of reactions for selected start steps of the pyrolysis of CPD. The molecular‐assisted hydrogen transfer under formation of cyclopentadienyl and cyclopentenyl radicals ought to be one of the most important reaction steps.

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.

ChemInform Abstract: Spin Trapping of Cyclopentadienyl Radicals Using Nitroso Compounds and Nitrones

Chemischer InformationsdienstVolume 17, Issue 19 Preparative Organic Chemistry ChemInform Abstract: Spin Trapping of Cyclopentadienyl Radicals Using Nitroso Compounds and Nitrones P. J. BARKER, P. J. BARKERSearch for more papers by this authorS. R. STOBART, S. R. STOBARTSearch for more papers by this authorP. R. WEST, P. R. WESTSearch for more papers by this author P. J. BARKER, P. J. BARKERSearch for more papers by this authorS. R. STOBART, S. R. STOBARTSearch for more papers by this authorP. R. WEST, P. R. WESTSearch for more papers by this author First published: May 13, 1986 https://doi.org/10.1002/chin.198619155AboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume17, Issue19May 13, 1986 RelatedInformation

Spin trapping of cyclopentadienyl radicals using nitroso compounds and nitrones

Cyclopentadienyl radicals C5H4X˙(X = H or Me) generated in various solvents either chemically or photochemically from Hg(C5H4X)2 have been trapped using nitrosodurene (ND), pheny(t-butyl)nitrone (PBN), and 3,4-dihydro-2,2-dimethyl-2H-pyrrole N-oxide (DMPO) to afford radical adducts identifiable by e.s.r. spectroscopy. For X = H the ND adduct (1) gives rise to a six-line e.s.r. spectrum in toluene having a(N)ca. 13.5 G and a(H)ca. 6.5 G. In contrast, production of (1) by photolysis in CHCl3 is accompanied by the appearance of a species (7) with a four-line e.s.r. spectrum, assigned to the H˙/ND (aminoxyl) adduct. For X = Me, with ND as spin trap, overlapping e.s.r. spectra which correspond to adduct formation at points of maximum spin-density [C(1) and C(3), C(4)] are resolved. Similar spin trapping of radicals derived photolytically from C5Me5H is also described.

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.

Reaction of phosphonyl radicals with sterically hindered carbonyl compounds

1. Phosphonyl radicals add to di-tert-butyl-p-benzoquinone either at the carbonyl O atom to form a phenoxyl radical, or at the multiple bond of the ring to form a cyclopentadienyl radical. The reaction of phosphonyl radicals with sterically hindered methylenequinones proceeds in a similar way. 2. Phosphonyl radicals add to 4,4-dialkyl-2,6-di-tert-butyl-2,5-cyclohexadien-1-ones at the ring multiple bond only to form the corresponding cyclopentadienyl radicals. 3. Phosphonyl radicals add to 3,3,5,5-tetra-tert-butyldiphenoquinone at the multiple bond of the ring at the 1(1) and 2(2) positions, and to the O atom to form the corresponding radicals.

Carbon-13, fluorine-19, and proton ENDOR investigations of substituent effects on lifting of orbital degeneracy in cyclopentadienyl radicals. Syntheses

Carbon-13, fluorine-19, and proton ENDOR investigations of substituent effects on lifting of orbital degeneracy in cyclopentadienyl radicals. Syntheses

An ESR study of the photolysis of cyclopentadienylzirconium compounds

ESR spectroscopy has been used to study the photolysis of the compounds (C 5H 5) 2ZrCl 2, (Me 5C 5) 2ZrCl 2, (C 5H 5) 2ZrMe 2, (C 5H 5) 2ZrMeCl and (C 5Me 5) 2ZrMe 2 With the first two compounds, the primary reaction is the loss of the cyclopentadienyl radical, and with the second two it is the loss of the methyl radical, but from (C 5Me 5) 2ZrMe 2, both the cyclopentadienyl and methyl radicals could be identified. In every case, the spectrum of a zirconium(III) radical could be observed at high field, but frequently this could be resolved into a doublet, indicating the formation of an unidentified zirconium(III) hydride. Various reagents were added to intercept the initially formed zirconium(III) species, and the following spin adducts have been identified with varying degrees of certainty: C 5H 5Zr(Cl 2)OO •, Me 5C 5Zr(Cl 2)OO •, C 5H 5Zr(Cl 2)ON(Bu t)O •, (C 5H 5) 2Zr(Cl)ON and 2,5-Bu t 2-6[(C 5H 5)Zr(Me 2)O]C 6H 2O •.

Radicals and Radical Ions Derived from 1,3‐Dienes

AbstractRecent improvements in experimental methods have made it possible to generate radicals and radical ions derived from simple 1,3‐dienes, so that their e.s.r. spectra can be observed in fluid solution.Photolysis of various cyclopentadienylmetallic compounds, or even of pentamethylcyclopentadiene itself, serves as a source of the corresponding cyclopentadienyl radicals, and the former method can be extended to the preparation of the fulvalene and pentalene radical anions.Cyclobutadiene radical cations are formed when the complexes formed between dimerised dialkylalkynes and aluminium chloride are photolysed. Di‐t‐butyl‐ethyne may also undergo a double nucleophilic rearrangement when it is treated with aluminium chloride, resulting in the formation of the hexamethylbutadiene radical cation, which can also be prepared from hexamethylbutadiene itself.Radical anions and cations can be regarded as being the conjugate bases and acids, respectively, of neutral radicals, and this principle has been exploited in the generation of cyclopentadiene radical cations from the photolysis of cyclopentadienes in acid solution.

Alkyl and silyl derivatives of benzene radical-cations formed by radiolysis: an electron spin resonance study

Exposure of dilute solutions of various alkyl- and silyl-benzenes in trichlorofluoromethane to 60Co γ-rays at 77 K gave species whose e.s.r. spectra are characteristic of substituted benzene cations. For the ethyl derivative large hyperfine coupling to the methyl protons establishes a preferred conformation in which the methyl group lies in the plane of the benzene ring. For the isopropyl derivative, and particularly for p-cymene cations, several conformers were detected, the sterically most favourable being the least stable. This is interpreted in terms of strong electron-donation from the C–H σ-orbitals into the ring π-orbital with is greater than that from C–Me σ-orbitals so that π-overlap with the C-H bonds is maximised. The energy difference is slightly greater than the steric energy differences. The SOMO for the silyl derivatives (SiH3, SiHMe2, and SiMe3) is also the a1 orbital (ψa) which places maximum spin-density on the position of the substituent. However, the degree of hyperconjugation involving Si-H σ-orbitals is reduced by a factor of ca.2, as judged by the 1H hyperfine coupling constants. Nevertheless, it was not found necessary to invoke a mixture of the a1 and a2 orbitals (ψS and ψA) to explain the results. These results are compared with those for the corresponding radical-anions and for the neutral cyclopentadienyl radicals.

An ESR study of the photolysis of dicyclopentadienyltitanium dichloride

ESR spectroscopy has been used to monitor the radicals which are formed when dicyclopentadienyltitanium dichloride is photolysed in solution alone or in the presence of various reagents (oxygen, ethers, pyridine, phosphines, 2-methyl-2-nitropropane, nitrosodurene, biacetyl, and 3,6-di-t-butyl-1,2-benzoquinone). The direct observation of the spectrum of the cyclopentadienyl radical, and the unambiguous resolution of the hyperfine coupling by two chlorine atoms in the spin adduct which the titanium fragment forms with 2-methyl-2-nitropropane suggests that, at least in tetrahydrofuran, the principal reaction is, as commonly accepted: ▪ However, under some conditions (e.g. in ether solvent, or in the presence of pyridine, particularly at low temperatures), the spectra of two different titanium(III) radicals, with resolvable hyperfine structure, can be observed, and this simple model needs to be extended.

Excitation and emission spectra of the 2A″ 2 ↽ → 2E″ 1 system of the gas-phase cyclopentadienyl radical

Laser-induced fluorescence excitation and resolved emission spectra of the gas-phase cyclopentadienyl radical are reported. Emission spectra following single vibronic level excitation of prominent absorption features from 338.0 to 325.6 nm are recorded and catalogued. The collision-free fluorescence lifetime is in the range of 12–20 ns. Efficient vibrational relaxation of the 2A″ 2 state by SF 6 is reported. Based upon analysis of the excitation and emission spectra it is concluded that there are two or more Jahn-Teller active modes in C 5H 5. The measured spectra and our analyses agree qualitatively with recent calculations on C 5H 5 that assume three active modes with Jahn-Teller coupling parameters, λ 2 of 0.6–1.9.

ChemInform Abstract: AN ELECTRON SPIN RESONANCE STUDY OF THE EFFECT OF GROUP IV SUBSTITUENTS IN CYCLOPENTADIENYL RADICALS

Chemischer InformationsdienstVolume 13, Issue 37 Physical Organic Chemistry ChemInform Abstract: AN ELECTRON SPIN RESONANCE STUDY OF THE EFFECT OF GROUP IV SUBSTITUENTS IN CYCLOPENTADIENYL RADICALS P. J. BARKER, P. J. BARKERSearch for more papers by this authorA. G. DAVIES, A. G. DAVIESSearch for more papers by this authorR. HENRIQUEZ, R. HENRIQUEZSearch for more papers by this authorJ.-Y. NEDELEC, J.-Y. NEDELECSearch for more papers by this author P. J. BARKER, P. J. BARKERSearch for more papers by this authorA. G. DAVIES, A. G. DAVIESSearch for more papers by this authorR. HENRIQUEZ, R. HENRIQUEZSearch for more papers by this authorJ.-Y. NEDELEC, J.-Y. NEDELECSearch for more papers by this author First published: September 14, 1982 https://doi.org/10.1002/chin.198237054Read the full textAboutPDF 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 onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume13, Issue37September 14, 1982 RelatedInformation

ChemInform Abstract: SYNTHESIS OF FERROCENYLRUTHENOCENE

AbstractDie zweikernige Titelverbindung (III) wird durch Ullmann‐Kupplung von (II) mit einem großen Überschuß an Iodferrocen (I) in geschmolzener Phase synthetisiert.