JEE Chemistry 2024 Question with Solution

Given: Assertion $A$ states that aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom. Reason $R$ states that phenols react with halogen acids violently.

Find: Which option correctly describes the truth values of $A$ and $R$.

Assertion $A$ is true. In phenol, the $-OH$ group is attached to an aromatic ring, and the bond acquires resonance stabilization with the benzene ring. Because of this, direct replacement of the hydroxyl group by a halogen atom does not occur easily.

Reason $R$ is false. Phenols do not react violently with halogen acids such as $\text{HCl}$, $\text{HBr}$, or $\text{HI}$ under normal conditions to give aryl halides by simple replacement of the hydroxyl group.

Therefore, assertion $A$ is true but reason $R$ is false. The correct option is C.

Given:

• Assertion $A$: Aryl halides cannot be prepared by replacement of hydroxyl group of phenol by halogen atom.
• Reason $R$: Phenols react with halogen acids violently.

Find: The correct relation between assertion and reason.

1. Analyze Assertion $A$: Phenols have a hydroxyl group attached directly to the benzene ring. The $-OH$ group is resonance stabilized, so the $\text{C}-\text{O}$ bond is strengthened and is not easily broken for substitution by halide ion.
2. Hence, direct conversion of phenol into aryl halide by replacing $-OH$ with halogen is not feasible by the usual halogen acid method.
3. Therefore, Assertion $A$ is true.
4. Analyze Reason $R$: The statement says phenols react violently with halogen acids. This is incorrect. Phenols generally do not undergo such reaction with halogen acids to form aryl halides.
5. Therefore, Reason $R$ is false.

A representative statement from the solution is:

Thus, the final conclusion is that Assertion $A$ is true but Reason $R$ is false, so the correct option is C.