(a) Draw the three isomers of benzenedicarboxylic acid.
(b) The isomers have melting points of 210°C, 343°C, and 427°C. Nitration of the isomers at all possible positions was once used to determine their structures. The isomer that melts at 210°C gives two mononitro isomers. The isomer that melts at 343°C gives three mononitro isomers. The isomer that melts at 427°C gives only one mononitro isomer. Show which isomer has which melting point