JEE Chemistry 2023 Question with Solution

Given: The molecular formula is $\mathrm{C_8H_{11}N}$ and the compounds must be aromatic amines obtainable by Gabriel phthalimide synthesis.

Find: The number of isomeric aromatic amines possible.

Gabriel phthalimide synthesis is used to prepare primary amines, that is, compounds of the form $\mathrm{R-NH_2}$. Therefore, we must count only those isomeric primary aromatic amines having formula $\mathrm{C_8H_{11}N}$.

The degree of unsaturation is:

A degree of unsaturation of $\mathrm{4}$ indicates the presence of a benzene ring.

After accounting for the benzene ring, the remaining composition corresponds to a total of two carbon atoms outside the ring framework. Since the product must be a primary amine, the nitrogen must appear as $\mathrm{-NH_2}$ in the allowed structures.

The listed ring-substituted dimethylaniline representations must be counted with symmetry taken into account. As stated in the solution, some apparently different dimethylanilines are actually identical by symmetry, so they are not counted separately.

Therefore, the total number of possible isomeric aromatic amines that can be synthesized by Gabriel phthalimide synthesis is $6$.

Given: Molecular formula $\mathrm{C_8H_{11}N}$.

Find: How many isomeric aromatic primary amines satisfy this formula and can be prepared by Gabriel phthalimide synthesis.

First use the unsaturation count:

Substituting the values:

A value of $\mathrm{DU = 4}$ is consistent with one benzene ring. Hence the compounds are aromatic and contain a benzene nucleus.

Now apply the condition from Gabriel phthalimide synthesis: it gives primary amines. So structures in which nitrogen is not present as $\mathrm{-NH_2}$ are excluded.

The valid isomers then include the possible aromatic primary amines with the required carbon count, including benzylamine-type and ring-substituted aniline-type arrangements, while equivalent substitution patterns are identified and merged.

Hence, after eliminating equivalent structures produced by ring symmetry, the final count is $6$.