Issue Date: February 23, 2009
Elusive Biradical Spotted
Australian researchers may have experimental evidence for a long-sought biradical intermediate thought to occur in bioluminescent and chemiluminescent light-producing reaction pathways (J. Am. Chem. Soc., DOI: 10.1021/ja808401p). Scientists first suggested the existence of the dioxy biradical in the thermal decomposition of 1,2-dioxetanes more than 30 years ago. But the species has never been experimentally confirmed. Neil W. Barnett of Deakin University, in Victoria, and coworkers used electron paramagnetic resonance (EPR) spectroscopy to monitor the decomposition of the related chemiluminescence intermediate 1,2-dioxetanedione during the reaction of oxalyl chloride and hydrogen peroxide in the presence of 9,10-diphenylanthracene at 180 K. EPR spectra show resonances consistent with the formation of a biradical. However, measurements at such low temperatures may not be sufficient. "Until one obtains direct spectroscopic evidence at room temperature for the intermediate, rather casually referred to for years as dioxetanedione, doubts will persist that observations like those reported in the paper and the real world can be connected," says Douglas C. Neckers, a photochemist at Ohio's Bowling Green State University.
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