Question

The reaction of \( (R)-2-bromobutane \) with CN\(^-\) proceeds by ..........

• A. retention of configuration
• B. inversion of configuration
• C. formation of CH\(_3\)-CH(CH\(_2\))CH\(_2\)
• D. formation of (S)-2-methylbutanenitrile

Hint:

In an SN2 reaction, the nucleophile attacks from the opposite side of the leaving group, causing inversion of configuration at the chiral center.

Answer 1

The Correct Option is B, D

Step 1: Understanding nucleophilic substitution.
In nucleophilic substitution reactions (SN1 and SN2), when a nucleophile like CN\(^-\) attacks a chiral carbon, the configuration of the carbon can invert in the case of an SN2 reaction. For \( (R)-2-bromobutane \), the CN\(^-\) will attack the electrophilic carbon, leading to inversion of configuration.
Step 2: Analyzing the options.
(A) retention of configuration: Incorrect — Retention of configuration is characteristic of SN1 reactions, not SN2.
(B) inversion of configuration: Correct — The CN\(^-\) nucleophile will cause inversion of configuration in this SN2 reaction.
(C) formation of CH\(_3\)-CH(CH\(_2\))CH\(_2\): Incorrect — This is a product that does not match the reaction.
(D) formation of (S)-2-methylbutanenitrile: Incorrect — The product is correct in terms of structure but does not match the configuration change (inversion is expected).
Step 3: Conclusion.
The correct answer is (B) inversion of configuration, as the reaction proceeds by an SN2 mechanism, causing inversion of configuration.