Solvent effect on the sensitized photooxygenation of cyclic and acyclic α-diimines

Else Lemp, Antonio L. Zanocco, German Günther, Nancy Pizarro

Resultado de la investigación: Article

11 Citas (Scopus)

Resumen

The reaction of singlet molecular oxygen with a series of cyclic and acyclic α-diimines was studied. Time-resolved methods were used to measure total reaction rate constants and steady-state methods were used to determine chemical reaction rate constants. GC-MS was used to tentatively assign the reaction products. 5,6-Disubstituted cyclic α-diimines are singlet oxygen quenchers, but become more effective in polar solvents. A reaction mechanism involving a perepoxide intermediate or transition state leading to a hydroperoxide seems to be a key reaction path for product formation. A replacement of the phenyl substituent for a methyl substituent opens up an additional reaction involving a perepoxide-like exciplex, which increases singlet oxygen quenching of the cyclic α-diimines. The reactivity of 5,6-disubstituted cyclic α-diimines towards singlet oxygen is highly dependent on steric interactions arising from vicinal phenyl rings and from electronic effects. 1,4-Disubstituted acyclic α-diimines are, by comparison, moderate or poor singlet oxygen quenchers. Total rate constants are scarcely dependent on solvent properties, but instead correlate with the Hildebrand parameter. These results are explained in terms of a mechanism involving a dioxetane-like exciplex that gives rise to a charged intermediate leading to products.

Idioma originalEnglish
Páginas (desde-hasta)10734-10746
Número de páginas13
PublicaciónTetrahedron
Volumen62
N.º46
DOI
EstadoPublished - 13 nov 2006

Huella dactilar

Singlet Oxygen
Rate constants
Reaction rates
Molecular oxygen
Reaction products
Hydrogen Peroxide
Chemical reactions
Quenching

ASJC Scopus subject areas

  • Biochemistry
  • Drug Discovery
  • Organic Chemistry

Citar esto

Lemp, Else ; Zanocco, Antonio L. ; Günther, German ; Pizarro, Nancy. / Solvent effect on the sensitized photooxygenation of cyclic and acyclic α-diimines. En: Tetrahedron. 2006 ; Vol. 62, N.º 46. pp. 10734-10746.
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Solvent effect on the sensitized photooxygenation of cyclic and acyclic α-diimines. / Lemp, Else; Zanocco, Antonio L.; Günther, German; Pizarro, Nancy.

En: Tetrahedron, Vol. 62, N.º 46, 13.11.2006, p. 10734-10746.

Resultado de la investigación: Article

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AB - The reaction of singlet molecular oxygen with a series of cyclic and acyclic α-diimines was studied. Time-resolved methods were used to measure total reaction rate constants and steady-state methods were used to determine chemical reaction rate constants. GC-MS was used to tentatively assign the reaction products. 5,6-Disubstituted cyclic α-diimines are singlet oxygen quenchers, but become more effective in polar solvents. A reaction mechanism involving a perepoxide intermediate or transition state leading to a hydroperoxide seems to be a key reaction path for product formation. A replacement of the phenyl substituent for a methyl substituent opens up an additional reaction involving a perepoxide-like exciplex, which increases singlet oxygen quenching of the cyclic α-diimines. The reactivity of 5,6-disubstituted cyclic α-diimines towards singlet oxygen is highly dependent on steric interactions arising from vicinal phenyl rings and from electronic effects. 1,4-Disubstituted acyclic α-diimines are, by comparison, moderate or poor singlet oxygen quenchers. Total rate constants are scarcely dependent on solvent properties, but instead correlate with the Hildebrand parameter. These results are explained in terms of a mechanism involving a dioxetane-like exciplex that gives rise to a charged intermediate leading to products.

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