problemS
(1) Before spectroscopy was invented, Korner's absolute method was 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-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. 

(2) Before spectroscopy was invented, Korner's absolute method was 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-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 structures for the three nitrated isomers. (Draw all three compounds.) 

(3) Propose a structure consistent with the following NMR spectra and this additional information: Elemental analysis shows the molecular formula to be C8H7ClO. The IR spectrum shows a moderate absorption at 1602 cm-1 and a strong absorption at 1690 cm-1. 

(4) Propose a structure consistent with the following NMR spectra and this additional information: The mass spectrum shows a double molecular ion of ratio 1:1 at m/z 184 and 186. 

(5) Anions of hydrocarbons are rare, and dianions of hydrocarbons are extremely rare. The following hydrocarbon reacts with two equivalents of butyllithium to form a dianion of formula [C8H6]2- . Propose a structure for this dianion. Why does it form so readily?