Question

Optically active alkyl halide undergoing S\(_N\)2 substitution involves

• A. retention of configuration
• B. racemic mixture
• C. inversion of configuration
• D. formation of carbocation

Hint:

In the S\(_N\)2 reaction, the key feature is the backside attack by the nucleophile, resulting in an inversion of configuration at the electrophilic carbon.

Answer 1

The Correct Option is C

Step 1: Understanding S\(_N\)2 mechanism.
In the S\(_N\)2 (bimolecular nucleophilic substitution) mechanism, the nucleophile attacks the electrophilic carbon from the opposite side of the leaving group, resulting in the inversion of configuration. This happens because the nucleophile attacks from the backside, causing a flip in the configuration of the molecule.
Step 2: Evaluate each option.
- Option 1: Retention of configuration: Retention of configuration occurs in the S\(_N\)1 mechanism, where the intermediate carbocation can undergo either attack from the nucleophile on the same side or opposite side, leading to retention or inversion. It does not occur in the S\(_N\)2 mechanism.
- Option 2: Racemic mixture: A racemic mixture is typically formed in the S\(_N\)1 mechanism due to the possibility of nucleophilic attack from either side of the planar carbocation. However, in S\(_N\)2, only inversion of configuration occurs, not a racemic mixture.
- Option 3: Inversion of configuration: This is the correct answer. In the S\(_N\)2 mechanism, the nucleophile attacks the carbon from the opposite side of the leaving group, causing an inversion of the configuration.
- Option 4: Formation of carbocation: Carbocation formation is a key feature of the S\(_N\)1 mechanism, not the S\(_N\)2 mechanism. In S\(_N\)2, there is no formation of a carbocation.
Step 3: Conclusion.
The optically active alkyl halide undergoing S\(_N\)2 substitution involves inversion of configuration.
Final Answer: \[ \boxed{\text{The correct answer is inversion of configuration.}} \]