Answer :
Final answer:
The isomer that melts at 210°C and gives two mononitro isomers is phthalic acid; the one at 343°C giving three mononitro isomers is isophthalic acid; and the one melting at 427°C yielding a single mononitro isomer is terephthalic acid.
Explanation:
The melting points of benzene dicarboxylic acid isomers are indicative of their structural differences. The three isomers in question are phthalic (o-benzene dicarboxylic), isophthalic (m-benzene dicarboxylic), and terephthalic (p-benzene dicarboxylic) acids, which refer to the ortho, meta, and para isomers, respectively.
The isomer with a melting point of 210 degrees Celsius that yields two mononitro isomers upon nitration is the phthalic acid. The ortho position allows for two substitutable positions that are not equivalent, hence two possible mononitro products.
The isomer with a melting point of 343 degrees Celsius provides three mononitro isomers, which is characteristic of the isophthalic acid, the meta isomer. Each of the carboxylic acid groups has two positions for substitution, but one of them is shared, leading to three unique products.
The isomer with the highest melting point, at 427 degrees Celsius, that forms only one mononitro isomer upon nitration is the terephthalic acid, the para isomer. In this symmetrical molecule, nitration at either of the two equivalent sites yields the same compound, resulting in only one product.
Melting points can be a powerful identification tool for determining structures of organic compounds, provided their purity is confirmed by methods such as mixed melting point determination.
