Question

Identify the major product \((P)\) in the following reaction sequence: \[ (\text{CH}_3)_3\text{CBr} \xrightarrow[\Delta]{\text{Alcoholic KOH}} X \xrightarrow{\text{HBr}} P \]

• A. \((\text{CH}_3)_3\text{CBr}\)
• B. \((\text{CH}_3)_2\text{CHCH}_2\text{Br}\)
• C. \(\text{CH}_3 - \text{CH} - \text{CH} - \text{CH}_3\;(\text{with Br substituent on one of the middle carbons})\)
• D. \(\text{CH}_3 - \text{CH} = \text{CH} - \text{CH}_2\text{Br}\)

Hint:

Tertiary alkyl halides often undergo elimination (to form a tertiary alkene) followed by Markovnikov addition of HBr, leading back to the same tertiary bromide.

Answer 1

The Correct Option is A

Step 1: Elimination with Alcoholic KOH \begin{itemize} \item Tert-butyl bromide \((\text{CH}_3)_3\text{CBr}\) undergoes an \(E2\) elimination with alcoholic KOH to form 2-methylpropene \(\big(\text{CH}_2=C(\text{CH}_3)_2\big)\). \end{itemize} 

Step 2: Addition of HBr to the Alkene \begin{itemize} \item 2-Methylpropene reacts with HBr via Markovnikov addition, giving back the tertiary bromide, \((\text{CH}_3)_3\text{CBr}\). \item The reaction pathway results in the same tertiary haloalkane as the starting material. \end{itemize} Hence, the major product \((P)\) is \(\text{tert-butyl bromide}\), \((\text{CH}_3)_3\text{CBr}\).