Radicals and Stratospheric Ozone

How many atoms share the unpaired electron in semiquinone  

Using resonance structures, explain why a catechin is an antioxidant. 

Ozone (O3), a major constituent of smog, is a health hazard at ground level— it inflames the airways, worsens lung ailments, and increases the risk of death from heart or lung disease. In the stratosphere, however, a layer of ozone shields the Earih from harmful solar radiation, with the greatest concentrations lying between 12 and 15 miles above the Earth s surface. 

The ozone layer is thinnest at the equator and densest toward the poles. Since about 1985, scientists have noted a precipitous drop in stratospheric ozone over Antarctica. This area of ozone depletion, dubbed the ozone hole, is unprecedented in the history of ozone observations. Scientists subsequently noted a similar decrease in ozone over Arctic regions then, in 1988, they detected a depletion of ozone over the United States for the first time. Three years later, scientists determined that the rate of ozone depletion was two to three times faster than originally anticipated. 

Strong circumstantial evidence implicated synthetic chlorofluorocarbons (CFCs)— alkanes in which all the hydrogens have been replaced by fluorine and chlorine—as a major cause of ozone depletion. These gases, known commercially as Freon, had been used extensively as cooling fluids in refrigerators and air conditioners. They were also once widely used as propellants in aerosol spray cans (deodorant, hair spray, and so on) because of their odorless, nontoxic, and nonflammable properties and because, being chemically inert, they do not react with the contents of the can. Now such use is banned and propane and butane are used as propellants instead. 

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