Question

Which of the following compounds will give racemic mixture on nucleophilic substitution by \( \text{OH}^- \) ion? \includegraphics[width=5cm]{71.png}

• A. \( (i) \)
• B. \( (i), (ii), and (iii) \)
• C. \( (ii) and (iii) \)
• D. \( (i) and (iii) \)

Hint:

Racemic mixtures form in \( \text{S}_\text{N}1 \) reactions due to the formation of a planar carbocation intermediate, which allows the nucleophile to attack from either side.

Answer 1

The Correct Option is B

Compounds undergoing \( \text{S}_\text{N}1 \) nucleophilic substitution yield a racemic mixture. This occurs due to the formation of a planar carbocation intermediate, susceptible to nucleophilic attack from either face, resulting in a 1:1 enantiomer ratio. The reactivity order for \( \text{S}_\text{N}1 \) reactions is: \[3^\circ>2^\circ>1^\circ \, \text{(alkyl halides)}.\]
Compound (i): Possesses a secondary carbon and proceeds via the \( \text{S}_\text{N}1 \) mechanism.
Compound (ii): Features a tertiary carbon and strongly favors the \( \text{S}_\text{N}1 \) mechanism.
Compound (iii): Contains a secondary carbon and follows the \( \text{S}_\text{N}1 \) mechanism. Consequently, all three compounds will yield a racemic mixture.
Final Answer:\[\boxed{(i), (ii), \text{and} (iii)}\]