Question

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Synthesis of ethyl phenyl ether may be achieved by Williamson synthesis.
Reason (R): Reaction of bromobenzene with sodium ethoxide yields ethyl phenyl ether.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

For Williamson synthesis of mixed ethers (especially those with an aryl group), always choose the phenoxide as the nucleophile and the alkyl halide as the electrophile. Never use an aryl halide as the electrophile in a Williamson synthesis.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
We need to evaluate the correctness of an Assertion and a Reason related to the Williamson ether synthesis.
Step 2: Key Formula or Approach:
The Williamson ether synthesis is a method for preparing ethers via an S\(_N\)2 reaction between a sodium alkoxide (or phenoxide) and an alkyl halide. \[ \text{R-O}^-\text{Na}^+ + \text{R'-X} \rightarrow \text{R-O-R'} + \text{NaX} \] For the S\(_N\)2 mechanism to be effective, the alkyl halide (R'-X) should ideally be primary or secondary. Aryl halides and tertiary alkyl halides are unreactive under S\(_N\)2 conditions.
Step 3: Detailed Explanation:
Analysis of Assertion (A):
"Synthesis of ethyl phenyl ether may be achieved by Williamson synthesis."
Ethyl phenyl ether has the structure C\(_6\)H\(_5\)-O-CH\(_2\)CH\(_3\). To synthesize this, we need a phenoxide part and an ethyl part. The correct strategy for Williamson synthesis is to use the phenoxide as the nucleophile and the alkyl halide as the electrophile. \[ \underbrace{\text{C}_6\text{H}_5\text{O}^-\text{Na}^+}_{\text{Sodium phenoxide}} + \underbrace{\text{CH}_3\text{CH}_2\text{Br}}_{\text{Ethyl bromide (1°)}} \rightarrow \text{C}_6\text{H}_5\text{-O-CH}_2\text{CH}_3 + \text{NaBr} \] This reaction works well because ethyl bromide is a primary alkyl halide, which is excellent for S\(_N\)2 reactions. Therefore, Assertion (A) is a correct statement.
Analysis of Reason (R):
"Reaction of bromobenzene with sodium ethoxide yields ethyl phenyl ether."
This statement describes the alternative combination of reagents: \[ \underbrace{\text{C}_6\text{H}_5\text{Br}}_{\text{Aryl halide}} + \underbrace{\text{CH}_3\text{CH}_2\text{O}^-\text{Na}^+}_{\text{Sodium ethoxide}} \rightarrow \text{No reaction} \] This reaction does not occur. S\(_N\)2 substitution is not feasible on an aryl halide like bromobenzene. This is because:
The carbon atom of the C-Br bond is sp\(^2\)-hybridized and less susceptible to nucleophilic attack.
The C-Br bond has partial double-bond character due to resonance with the benzene ring, making it stronger and harder to break.
The bulky and electron-rich benzene ring sterically hinders and electrostatically repels the incoming nucleophile.
Therefore, Reason (R) is an incorrect statement.
Step 4: Final Answer:
The Assertion (A) is correct, but the Reason (R) is incorrect. This corresponds to option (C).