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Titolo:
Substituent effects in pericyclic reactions of radical cations: The ring opening of 3-substituted cyclobutene radical cations
Autore:
Swinarski, DJ; Wiest, O;
Indirizzi:
Univ Notre Dame, Dept Chem & Biochem, Notre Dame, IN 46556 USA Univ Notre Dame Notre Dame IN USA 46556 Biochem, Notre Dame, IN 46556 USA
Titolo Testata:
JOURNAL OF ORGANIC CHEMISTRY
fascicolo: 20, volume: 65, anno: 2000,
pagine: 6708 - 6714
SICI:
0022-3263(20001006)65:20<6708:SEIPRO>2.0.ZU;2-F
Fonte:
ISI
Lingua:
ENG
Soggetto:
DIELS-ALDER REACTION; ELECTRON-TRANSFER; AB-INITIO; DNA PHOTOLYASE; ELECTROCYCLOREVERSION; CLEAVAGE;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Life Sciences
Physical, Chemical & Earth Sciences
Citazioni:
42
Recensione:
Indirizzi per estratti:
Indirizzo: Wiest, O Univ Notre Dame, Dept Chem & Biochem, Notre Dame, IN 46556 USA Univ Notre Dame Notre Dame IN USA 46556 Notre Dame, IN 46556 USA
Citazione:
D.J. Swinarski e O. Wiest, "Substituent effects in pericyclic reactions of radical cations: The ring opening of 3-substituted cyclobutene radical cations", J ORG CHEM, 65(20), 2000, pp. 6708-6714

Abstract

The substituent effects on the ring-opening reaction of cyclobutene radical cations have been studied at the Becke3LYP/6-31G* level of theory. The effect on the reaction energies and activation energies of the concerted and stepwise pathways of electron-donating substituents such as methyl and methoxy as well as electron-withdrawing substituents such as nitrile and carboxaldehyde in the 3-position of the cyclobutene is discussed. The exothermicity of the reaction correlates well with the ability of the substituent to stabilize the 1,3-butadiene radical cation by electron donation or conjugation; The relative stability of the (E) and (Z) isomers of the resulting 1,3-butadiene radical cations depends largely on steric effects. Similarly, steric effects are responsible for the relative energies of the different diastereomeric transition structures. The cyclopropyl carbinyl intermediate of the stepwise pathway resembles the nonclassical carbocation and is stabilized by electron-donating substituents. In the case of electron-donating substituents, this species becomes a minimum on the potential energy hypersurface, whereas unstabilized or destabilized cyclopropyl carbinyl radical cations are not minima on the hypersurface. The stabilization of the cyclopropylcarbinyl radical cation by substituents correlates qualitatively with the Brown-Okamoto substituent parameter sigma(+). However, in all cases studiedhere, the concerted mechanism is the lowest energy pathway.

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Documento generato il 04/12/20 alle ore 16:26:12