Before spectroscopy was invented, Korner's absolute method had been used to determine whether a disubstituted benzene derivative was the ortho, meta, or para isomer. Korner's method involves adding a third group (often a nitro group) and determining how many isomers are formed. A turn-of-the-20th-century chemist isolated an aromatic compound of molecular formula C6H4Br2. He carefully nitrated this compound and purified three isomers of formula C6H3Br2NO2, one of which was obtained in very small amounts. Propose a structure for the original compound.