JEE Chemistry 2026 Question with Solution

Given: Benzene first reacts with $\mathrm{Br_2/FeBr_3}$ to form compound $A$, and then $A$ undergoes nitration with concentrated $\mathrm{HNO_3/H_2SO_4}$ to give products $B$ and $C$.

Find: The method used for separation of the mixture of products $B$ and $C$.

Concept: Electrophilic substitution reactions on benzene often give mixtures of positional isomers. The choice of separation technique depends on physical properties such as volatility, solubility in water, and difference in boiling points.

Step 1: Identify compound $A$.

Step 2: Nitration of bromobenzene. Bromobenzene undergoes nitration with concentrated $\mathrm{HNO_3/H_2SO_4}$. Since bromine is an ortho-para directing group, nitration gives ortho-nitrobromobenzene $\text{(B)}$ and para-nitrobromobenzene $\text{(C)}$.

Thus, $B$ and $C$ are positional isomers.

Step 3: Compare physical properties of $B$ and $C$. Ortho-nitrobromobenzene is steam volatile, whereas para-nitrobromobenzene is less volatile due to better molecular packing and higher melting point.

This difference in volatility makes steam distillation an effective separation method.

Step 4: Eliminate other options.

• Simple distillation: Boiling points are too close for efficient separation.
• Fractional distillation: Not ideal here because the key difference is steam volatility.
• Sublimation: Neither compound readily sublimes.

Therefore, the correct option is D and the separation method is Steam distillation.

Given: Products $B$ and $C$ are formed after bromination followed by nitration of benzene.

Find: Which separation method is suitable.

A bromine substituent directs nitration to the ortho and para positions, so $B$ and $C$ are ortho and para isomers. Ortho-substituted aromatic compounds are often steam volatile because of weaker intermolecular interactions, while the para isomer usually packs better in the crystal lattice and is less volatile.

So, instead of comparing only boiling points, focus on steam volatility. Therefore, the correct option is D, Steam distillation.