Question

Identify `A' in the following reaction.

• A. A
• B. B
• C. C
• D. D

Hint:

A Grignard reagent on hydrolysis with water always gives the corresponding alkane. So, \(\mathrm{R-MgX}\) becomes \(\mathrm{R-H}\).

Answer 1

The Correct Option is B

Step 1: Formation of Grignard reagent.
The given compound is bromocyclohexane. When an alkyl halide reacts with magnesium in dry ether, it forms the corresponding Grignard reagent. Therefore, bromocyclohexane reacts with magnesium to give cyclohexyl magnesium bromide.
Step 2: Reaction of Grignard reagent with water.
Grignard reagents are highly reactive organometallic compounds. On treatment with water, the carbon-magnesium bond gets hydrolysed. As a result, the alkyl group attached to magnesium simply picks up a hydrogen atom.
\[ \mathrm{C_6H_{11}MgBr + H_2O \rightarrow C_6H_{12} + Mg(OH)Br} \] So, cyclohexyl magnesium bromide on hydrolysis gives cyclohexane.
Step 3: Analysis of the options.

• (A) Cyclohexadiene: Incorrect. Hydrolysis of a Grignard reagent does not produce a diene.
• (B) Cyclohexane: Correct. The Grignard reagent gives the corresponding alkane on hydrolysis.
• (C) Cyclohexanol: Incorrect. Alcohol would be formed only if the Grignard reagent reacted with oxygen-containing compounds like aldehydes, ketones, or epoxides before hydrolysis.
• (D) Cyclohexene: Incorrect. Hydrolysis does not lead to alkene formation in this reaction.

Step 4: Conclusion.
Hence, the product `A' formed after hydrolysis of cyclohexyl magnesium bromide is cyclohexane.
Final Answer:Cyclohexane.