1,n-Radical ions. Photosensitized (electron transfer) and electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane

The photosensitized (electron transfer) and the electrochemical oxidation of 1,1,2,2-tetraphenylcyclopropane (1) have been studied. The products obtained from the photosensitized (electron transfer) study are 1,1,3,3-tetraphenylpropene (2), 1,3,3-triphenylindene (3), tetraphenylallene (4), and 3-methoxy-1,1,3,3-tetraphenylpropene (8). The product ratios are dramatically dependent upon the reaction conditions, particularly sensitizer (aromatic nitriles, tetracyanoethylene, chloranil, and 2,3-dichloro-5,6-dicyanobenzoquinone were used), and solvent. The variations in product ratios are attributed to variations in the redox behaviour of the sensitizer radical anion and upon the basicity and nucleophilicity of the medium. The products in the electrochemical study are 3, 4, and 8. Common intermediates have been identified and a mechanism for the formation of products is proposed.

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Radical ions in photochemistry. 18. The photosensitized (electron transfer) tautomerization of alkenes; the 1,1-diphenyl alkene system

Canadian Journal of Chemistry ◽

10.1139/v87-384 ◽

1987 ◽

Vol 65 (9) ◽

pp. 2312-2314 ◽

Cited By ~ 5

Author(s):

Donald R. Arnold ◽

Shelley A. Mines

Keyword(s):

Hydrogen Bond ◽

Electron Transfer ◽

Radical Cation ◽

Radical Anion ◽

Relative Rate ◽

Radical Cations ◽

Radical Ions ◽

Back Electron Transfer ◽

Ambident Anion ◽

Determining Factor

The photosensitized (electron transfer) irradiation of several conjugated 1,1-diphenyl alkenes, in acetonitrile with 1,4-dicyanobenzene or 1-cyanonapthalene as electron accepting sensitizer and 2,6-lutidine as base, leads essentially quantitatively to tautomerization to the less stable unconjugated isomer(s). The proposed mechanism for this reaction involves formation of the alkene radical cation and sensitizer radical anion followed by deprotonation of the radical cation, reduction of the resulting radical to the ambident anion by back electron transfer from the radical anion, and reprotonation. There are several steps in this mechanism that could control the ratio of isomers. Evidence is provided that, at least in some cases, it is the relative rate of deprotonation from the isomeric radical cations that is the determining factor. This rate is influenced by the conformation of the radical cation; the carbon–hydrogen bond involved in the deprotonation step must overlap with the singly occupied molecular orbital.

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Isoelectronic Radical Ions from Single-Electron Transfer Reactions: Direct Observation of Persistent Solvent-Separated Radical Anion/Radical Cation Pairs

Angewandte Chemie International Edition in English ◽

10.1002/anie.198406131 ◽

1984 ◽

Vol 23 (8) ◽

pp. 613-614 ◽

Cited By ~ 11

Author(s):

Wolfgang Kaim

Keyword(s):

Electron Transfer ◽

Radical Cation ◽

Direct Observation ◽

Radical Anion ◽

Anion Radical ◽

Single Electron ◽

Transfer Reactions ◽

Single Electron Transfer ◽

Radical Ions ◽

Electron Transfer Reactions

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Article

Canadian Journal of Chemistry ◽

10.1139/v99-185 ◽

1999 ◽

Vol 77 (10) ◽

pp. 1655-1670 ◽

Cited By ~ 1

Author(s):

Dino Mangion ◽

Donald R Arnold

Keyword(s):

Electron Transfer ◽

Photoinduced Electron Transfer ◽

Photochemical Reactions ◽

Transfer Mechanism ◽

Radical Ions ◽

Reaction Conditions ◽

Electron Transfer Mechanism ◽

Photochemical Reactivity ◽

Bond Homolysis

The photochemical reactivity of a series of 4-halobenzonitriles and 4-haloanisoles with 1,1-diphenylethene in a nucleophilic solvent (methanol) has been investigated. Analysis of the photochemical reactions involving the 4-halobenzonitriles revealed formation of alkene-methanol adducts, such as 1-methoxy-2,2-diphenylethane, 1-methoxy-2,2-diphenylethene, and 1,1-dimethoxy-2,2-diphenylethane, indicative of a photochemical electron-transfer mechanism. These products were not significant in the photochemical reactions involving the 4-haloanisoles. Both the 4-halobenzonitriles and the 4-haloanisoles produced an arene-alkene-methanol Markovnikov adduct, 1-aryl-2-methoxy-2,2-diphenylethane (aryl = 4-cyanophenyl or 4-methoxyphenyl). This compound was shown to undergo an acid-catalysed elimination to 1-aryl-2,2-diphenylethene under the reaction conditions, which subsequently underwent a 6pi-electrocyclization to the 3-substituted(cyano or methoxy)-9-phenylphenanthrene. Possible mechanisms for the observed reactivity are discussed and evaluated.Key words: photochemistry, photoinduced electron transfer, bond homolysis, radical ions, radicals, exciplexes.

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ChemInform Abstract: ISOELECTRONIC RADICAL IONS FROM SINGLE ELECTRON TRANSFER REACTIONS: DIRECT DETECTION OF STABLE, SOLVENT-SEPARATED RADICAL ANION/RADICAL CATION PAIRS

Chemischer Informationsdienst ◽

10.1002/chin.198448105 ◽

1984 ◽

Vol 15 (48) ◽

Author(s):

W. KAIM

Keyword(s):

Electron Transfer ◽

Radical Cation ◽

Radical Anion ◽

Anion Radical ◽

Direct Detection ◽

Single Electron ◽

Transfer Reactions ◽

Single Electron Transfer ◽

Radical Ions ◽

Electron Transfer Reactions

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Radical ions in photochemistry. 6. The photosensitized (electron transfer) ring opening of aryloxiranes

Canadian Journal of Chemistry ◽

10.1139/v78-490 ◽

1978 ◽

Vol 56 (23) ◽

pp. 2985-2993 ◽

Cited By ~ 64

Author(s):

Angelo Albini ◽

Donald R. Arnold

Keyword(s):

Electron Transfer ◽

Ring Opening ◽

Radical Anion ◽

Electron Acceptors ◽

Radical Ions ◽

Subsequent Formation ◽

Carbon Carbon Bond ◽

Back Electron Transfer ◽

Carbonyl Ylide ◽

Cis And Trans

The photosensitized (electron transfer) irradiation of cis- and trans-2,3-diphenyloxirane (1 and 2) led to cleavage of the oxirane carbon–carbon bond and subsequent formation of the carbonyl ylide. The resulting carbonyl ylides have been trapped with the dipolarophiles, acrylonitrile, maleonitrile, and fumaronitrile. The resulting isomeric tetrahydrofuran derivatives have been characterized. Sensitizers (electron acceptors) which are effective include 1,4-dicyanonaphthalene, 1,4-dicyanobenzene, dimethyl terephthalate, and methyl 4-cyanobenzoate; 1-cyanonaphthalene was not effective. The proposed mechanism involves formation and cleavage of the oxirane radical cation followed by back electron transfer from the sensitizer radical anion to give the carbonyl ylide. Electrochemical and photophysical evidence which supports the proposed mechanism was obtained.

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