Question

Which one of the following is a true statement with reference to reaction between 2-Bromo-2-methylpropane and aqueous KOH?

• A. The rate of reaction depends on the concentration of the haloalkane and the nucleophile \(OH^-\)
• B. The reaction occurs at a fast rate since the substrate is a tertiary alkyl halide and follows \(S_N1\) mechanism
• C. The reaction is not favoured by the presence of polar protic solvent
• D. The reaction occurs at a slow rate since it follows \(S_N2\) mechanism

Hint:

Tertiary alkyl halides undergo \(S_N1\) reactions because they form stable carbocations, and polar protic solvents increase the reaction rate.

Answer 1

The Correct Option is B

Step 1: Identify the substrate.
2-Bromo-2-methylpropane is a tertiary alkyl halide.
\[ (CH_3)_3CBr \]

Step 2: Determine the mechanism.
Tertiary alkyl halides favour \(S_N1\) mechanism due to formation of a stable tertiary carbocation.

Step 3: Rate law for \(S_N1\).
In \(S_N1\) mechanism, rate depends only on the concentration of substrate:
\[ \text{Rate} = k[\text{R-Br}] \]
Hence, it does not depend on nucleophile concentration.

Step 4: Role of solvent.
Aqueous KOH is a polar protic medium, which stabilizes the carbocation and favours \(S_N1\) reaction.

Step 5: Speed of reaction.
Since carbocation formation is easy in tertiary halides, the reaction is fast.

Step 6: Eliminate incorrect options.
(A) Incorrect: rate does not depend on nucleophile in \(S_N1\).
(C) Incorrect: polar protic solvents favour \(S_N1\).
(D) Incorrect: tertiary halides do not follow \(S_N2\).

Step 7: Final conclusion.
\[ \boxed{\text{The reaction is fast and follows } S_N1 \text{ mechanism}} \]