Stepwise Cycloreversion of Oxetane Radical Cations with Initial C−O Bond Cleavage

2002 ◽  
Vol 124 (23) ◽  
pp. 6532-6533 ◽  
Author(s):  
Miguel A. Miranda ◽  
M. Angeles Izquierdo
Keyword(s):  
Bond Cleavage ◽  
Radical Cations

ChemInform Abstract: Mechanistic Aspects of β-Bond-Cleavage Reactions of Aromatic Radical Cations

ChemInform ◽  
2010 ◽  
Vol 31 (27) ◽  
pp. no-no
Author(s):  
Enrico Baciocchi ◽  
Massimo Bietti ◽  
Osvaldo Lanzalunga
Keyword(s):  
Bond Cleavage ◽  
Radical Cations ◽  
Aromatic Radical ◽  
Cleavage Reactions

1,n-Radical ions. Photosensitized (electron transfer) carbon–carbon bond cleavage. Formation of 1,6-radical cations

1991 ◽  
Vol 69 (2) ◽  
pp. 225-233 ◽  
Author(s):  
Donald R. Arnold ◽  
Laurie J. Lamont ◽  
Allyson L. Perrott
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Bond Cleavage ◽  
Radical Cations ◽  
Dimethyl Acetal ◽  
Mercury Vapour ◽  
Carbon Bond ◽  
Carbon Carbon Bond ◽  
Mercury Vapour Lamp ◽  
Mm2 Calculations

The reactivity of the radical cations of methyl 2,2-diphenylcyclohexyl ether (7), 6,6-diphenyl-1,4-dioxaspiro[4.5]decane (8), methyl cis- and trans-2-phenylcyclohexyl ether (9cis and trans), and 6-phenyl-1,4-dioxaspiro[4.5]decane (10), generated by photosensitized (electron transfer) irradiation, has been studied. Solutions of the ethers and acetals in acetonitrile–methanol (3:1), with 1,4-dicyanobenzene (2) serving as the electron acceptor, were irradiated with a medium-pressure mercury vapour lamp through Pyrex. The diphenyl derivatives 7 and 8 were reactive; 7 gave 6,6-diphenylhexanal dimethyl acetal (11) and 8 gave 2-methoxy-2-(5,5-diphenylpentyl)-1,3-dioxolane (12). These are the products expected from the intermediate 1,6-radical cation, formed upon carbon–carbon bond cleavage of the cyclic radical cation. The monophenyl derivatives 9cis and trans and 10 were stable under these irradiation conditions. The mechanism for the carbon–carbon bond cleavage and for the cis–trans isomerization is discussed. An explanation, based upon conformation, is offered for the lack of reactivity of 9 and 10. Molecular mechanics (MM2) calculations were used to determine the preferred conformation of 9cis and trans, and 10. Key words: photosensitization, electron transfer, radical cation, carbon–carbon bond cleavage, conformation.

Theoretical examination of competitive β-radical-induced cleavages of N–Cα and Cα–C bonds of peptides

2015 ◽  
Vol 93 (12) ◽  
pp. 1355-1362 ◽  
Author(s):  
Wai-Kit Tang ◽  
Chun-Ping Leong ◽  
Qiang Hao ◽  
Chi-Kit Siu
Keyword(s):  
Amino Acid ◽  
Density Functional ◽  
Bond Cleavage ◽  
Radical Cations ◽  
Radical Center ◽  
Amino Acid Residues ◽  
Mobile Proton ◽  
Aromatic Side Chain ◽  
Heterolytic Cleavage ◽  
Terminal Fragment

Selective cleavages of N–Cα and Cα–C bonds of β-radical tautomers of amino acid residues in radical peptides have been examined theoretically by means of the density functional theory at the M06-2X/6-311++G(d,p) level. The majority of the bond cleavages are homolytic via β-scission. Their energy barriers depend largely on the ability of the radical being stabilized in the transition structures and the availability of a mobile proton in the vicinity of the β-radical center. The N–Cα bond is less favorably cleaved than the Cα–C bond (except Ser and Thr) for systems without a mobile proton. It is because, firstly, the homolytic cleavage is less favorable for the more polar N–Cα bond than for the less polar Cα–C bond. Secondly, a less stable σ-radical localized on the amide nitrogen atom of the incipient N-terminal fragment is formed for the former, while a more stable radical delocalized in a π*(CO)-like orbital of the incipient C-terminal fragment is formed for the latter. In the presence of a mobile proton N-terminal to the β-radical center, some degrees of heterolytic cleavage character, as preferred by the polar N–Cα bond, are observed. Consequently, its barrier is reduced. If the mobile proton is located at the C-terminal amide oxygen of the β-radical center, the Cα–C bond cleavage will be significantly suppressed. It is because the radical in the incipient C-terminal fragment becomes more localized as a σ-radical on the carbon atom of its protonated amide group. With basic amino acid residues, the Cα–C bond cleavage can be reactivated. Heterolytic cleavage of the polar N–Cα bond can be largely facilitated if a mobile proton N-terminal to the β-radical center is available and the radical in the incipient C-terminal fragment is sufficiently stabilized, for instance, by the aromatic side chain of Trp and Tyr. Therefore, cleavages of the N–Cα bond induced by the β-radical tautomer of Trp and Tyr are often preferred as compared with cleavages of the Cα–C bond in peptide radical cations containing mobile protons.

The effect of meta- and para-methoxy substitution on the reactivity of the radical cations of arylalkenes and alkanes. Radical ions in photochemistry. Part 26

1991 ◽  
Vol 69 (5) ◽  
pp. 839-852 ◽  
Author(s):  
Donald R. Arnold ◽  
Xinyao Du ◽  
Kerstin M. Henseleit
Keyword(s):  
Electron Transfer ◽  
Radical Cation ◽  
Bond Cleavage ◽  
Cation Radical ◽  
Radical Cations ◽  
Addition Product ◽  
Molecular Orbital Calculations ◽  
Carbon Carbon Bond ◽  
Markovnikov Addition ◽  
Cis And Trans

The effect of meta- and para-methoxy substitution on the reactivity of some radical cations has been determined. The compounds chosen for study were 1-(3-methoxyphenyl)-1-phenylethylene (7), 1-(4-methoxyphenyl)-1-phenylethylene (8), 3-(3-methoxyphenyl)indene (9), 3-(4-methoxyphenyl)indene (10), methyl 2-(3-methoxyphenyl)-2-phenylethyl ether (11), methyl 2-(4-methoxyphenyl)-2-phenylethyl ether (12), cis- and trans-2-methoxy-1-(3-methoxyphenyl)indane (13), and cis- and trans-2-methoxy-1-(4-methoxyphenyl)indane (14). The radical cations of these compounds were generated by photosensitization (electron transfer) using 1,4-dicyanobenzene (3) as the electron acceptor. The three reactions studied were: (1) The addition of nucleophiles (methanol) to the radical cation of the arylalkenes, a reaction that yields the anti-Markovnikov addition product. (2) The carbon–carbon bond cleavage of radical cations, which yields products derived from the radical and carbocation fragments. (3) The deprotonation of the radical cation, a reaction that can be used to invert the configuration at a saturated carbon centre. The mechanisms of these reactions are discussed and the factors that need to be considered in order to predict reactivity are defined. Molecular orbital calculations (UHF/STO-3G) were carried out on the radical cations of the model compounds 3- and 4-vinylanisole and 3- and 4-methylanisole. Key words: photochemistry, photosensitize (electron transfer), radical cation, radical.

A Novel Role of Methanol in In-Cage Reaction of Radical Cations During Photosensitized C–C Bond Cleavage of 1,1,2,2-Tetraphenylethane

1992 ◽  
Vol 21 (5) ◽  
pp. 743-746 ◽  
Author(s):  
Katsuya Ishiguro ◽  
Toshihiko Osaki ◽  
Yasuhiko Sawaki
Keyword(s):  
Bond Cleavage ◽  
Radical Cations

Photoinduced electron transfer C—C bond cleavage reactions; oxidations and isomerizations

1984 ◽  
Vol 62 (3) ◽  
pp. 424-436 ◽  
Author(s):  
L. W. Reichel ◽  
G. W. Griffin ◽  
A. J. Muller ◽  
P. K. Das ◽  
Seyhan N. Ege
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Bond Cleavage ◽  
Radical Cations ◽  
Laser Flash ◽  
Time Resolved ◽  
Fragmentation Reactions ◽  
Oxidative Products

We have shown that radical cations generated by photoinduced electron transfer (ET) in 1,2-diarylethanes, aryl pinacols, and their derivatives undergo fragmentation reactions. In the presence of oxygen oxidative products are obtained. Time-resolved laser flash photolysis and other ancillary techniques have permitted us to define the mechanisms of certain oxidative processes observed.

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