Question

Identify the major product formed in the following reaction:

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

A Grignard reagent \((R{-}MgX)\) on hydrolysis with water always gives the corresponding hydrocarbon \((R{-}H)\). Remember: \[ R{-}MgX + H_2O \rightarrow R{-}H \]

Answer 1

The Correct Option is D

Step 1: Formation of HBr in situ.
When NaBr reacts with concentrated \(\mathrm{H_2SO_4}\), hydrogen bromide is generated: \[ \mathrm{NaBr + H_2SO_4 \rightarrow HBr + NaHSO_4} \] The HBr formed converts cyclohexanol into cyclohexyl bromide.
\[ \mathrm{C_6H_{11}OH + HBr \rightarrow C_6H_{11}Br + H_2O} \] Thus, the product after step (i) is cyclohexyl bromide.

Step 2: Formation of Grignard reagent.
Cyclohexyl bromide reacts with magnesium in dry ether to form the corresponding Grignard reagent: \[ \mathrm{C_6H_{11}Br + Mg \xrightarrow{dry\ ether} C_6H_{11}MgBr} \] This is cyclohexyl magnesium bromide.

Step 3: Hydrolysis of Grignard reagent.
Grignard reagents are highly reactive and on treatment with water undergo protonation: \[ \mathrm{C_6H_{11}MgBr + H_2O \rightarrow C_6H_{12} + Mg(OH)Br} \] The cyclohexyl group simply abstracts a proton from water to give the corresponding hydrocarbon.

Step 4: Identify the final product.
The hydrocarbon formed is cyclohexane: \[ \mathrm{C_6H_{12}} \] Therefore, the major product obtained after the complete sequence of reactions is cyclohexane.

Step 5: Final conclusion.
\[ \boxed{\text{Cyclohexane}} \] Hence, option (4) is the correct answer.