Biradical intermediates in the photoisomerization of dibenzodihydropentalenofurans to dibenzosemibullvalenes

Sajimon, Meledathu C. ; Ramaiah, Danaboyina ; Thomas, G. Kakkudiyil ; George, Manapurathu V. (2001) Biradical intermediates in the photoisomerization of dibenzodihydropentalenofurans to dibenzosemibullvalenes Journal of Organic Chemistry, 66 (9). pp. 3182-3187. ISSN 0022-3263

Full text not available from this repository.

Official URL:

Related URL:


The photoisomerization of a few substituted dibenzodihydropentalenofurans to the corresponding dibenzosemibullvalenes is reported. Steady-state photolysis of the dibenzodihydropentalenofurans 3a-d gave the corresponding dibenzosemibullvalenes 2a-d in nearly quantitative yields. The quantum yields of this photoisomerization were found to be in the range 0.17-0.26. Laser flash photolysis studies of the dibenzodihydropentalenofurans 3a-e showed transients, with absorption maxima around 410 nm and decaying by first-order kinetics. The lifetimes were in the range 14-30 μs in degassed benzene at 25°C. These transients were readily quenched (trapped) by molecular oxygen, and the Stern-Volmer quenching constants were found to be in the range (2.45-3.17) × 109 M-1 s-1. As a representative example, the 1,3-biradical intermediate from 3e was trapped by molecular oxygen to give the corresponding endoperoxide 11e. The transients were weakly quenched by triplet/radical quenchers such as 2,2,6,6-tetramethylpiperinyl-1-oxy (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperinyl-1-oxy (HTEMPO), and the quenching constants are found to be in the range (1.09-3.19) × 106 M-1 s-1. The decay rates of the transients were found to be temperature dependent and obeyed the Arrhenius equation. For example, the activation energy of the transient from 3a was ~4.5 kcal mol-1 and the Arrhenius preexponential factor log(A/s-1) for the decay of the transients was ~7.5. On the basis of our studies, these transients were assigned as the ground-state triplet biradicals, generated by the cleavage of the C-O bond of the starting dibenzodihydropentalenofurans.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
ID Code:12491
Deposited On:13 Nov 2010 13:28
Last Modified:31 May 2011 10:27

Repository Staff Only: item control page