Polychlorinated dibenzo-p-dioxins, or PCDDs, are highly toxic substances that are present in trace amounts as byproducts of some chemical manufacturing processes. They have been implicated in a number of environmental incidents€”for example, the chemical contamination at Love Canal and the herbicide spraying in Vietnam. The structure of dibenzo-p-dioxin, along with the customary numbering convention, is

The most toxic PCDD is 2,3,7,8-tetrachloro-dibenzo-p-dioxin. Draw the structure of this compound. Also draw the structures of two other isomers containing four chlorine atoms.

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