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Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde

Netto-Ferreira, J.C ; Scaiano, J.C

Canadian journal of chemistry, 1993-08, Vol.71 (8), p.1209-1215 [Periódico revisado por pares]

Ottawa, Canada: NRC Research Press

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  • Título:
    Laser flash photolysis study of the photochemistry of ortho-benzoylbenzaldehyde
  • Autor: Netto-Ferreira, J.C ; Scaiano, J.C
  • Assuntos: Chemistry ; Exact sciences and technology ; General and physical chemistry ; Photochemistry ; Physical chemistry of induced reactions (with radiations, particles and ultrasonics)
  • É parte de: Canadian journal of chemistry, 1993-08, Vol.71 (8), p.1209-1215
  • Descrição: Ketene-enols 4 and 5 have been generated by laser flash photolysis of ortho-benzoylbenzaldehyde ( 3 ) and kinetically and spectroscopically characterized. In benzene or acetonitrile, the E ketene-enol, 4 , shows absorption at 340 and 400 nm and a lifetime in excess of 1 ms, whereas the Z ketene-enol, 5 , shows maxima at 360 and 430 nm and a lifetime of only 1.5 μs. At shorter time scales we observed a weak absorption (λ max  = 580 nm) tentatively assigned to biradical 6 with a lifetime of 140 ns. The E ketene-enol is readily quenched by oxygen, dienophiles, methanol, and water, with quenching rate constants ranging from 3.6 × 10 3  M −1 s −1 (for methanol as a quencher) to 2.2 × 10 8  M −1 s −1 (for diethylketomalonate). At high water concentrations (typically > 10 M) a new species, 7 , was detected showing maximum absoiption at 510 nm and a growth lifetime of 7 μs. In deuterated water and using the same concentration as before we observed a formation lifetime for 7 of 10 μs, which results in an isotope effect of ~ 1.5. It is proposed that 5 is the main precursor for 7 . Steady-state irradiation of 3 in deaerated methanol leads to the formation of dihydroanthraquinone ( 9 ), a strongly colored and fluorescent (λ max  = 475 nm, τ n  = 29 ns) species, whereas 3-phenylphthalide ( 2 , R = Ph) is the main product when the irradiation is performed in benzene. Steady-state quenching of product formation by diethyl ketomalonate gives a Stern-Volmer constant of 380 M −1 from which we conclude that 5 is the ketene-enol responsible for product formation, in agreement with the laser flash photolysis results.
  • Editor: Ottawa, Canada: NRC Research Press
  • Idioma: Inglês
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