Question

(R)-2-Bromobutane is allowed to react with $NaI$ in acetone. The product formed is :

• A. trans-2-butane
• B. ($\pm$)-2-iodobutane
• C. (S)-2-iodobutane
• D. (R)-2-iodobutane

Answer 1

The correct option is C

(S)-2-iodobutane

$I^{\ominus }$ is a capable nucleophile. The given substrate - a secondary alkyl bromide - has a good enough leaving group. The solvent is polar aprotic and overall everything is conducive for an $S_{N}2$. Now let us explore the stereochemical implications; in $S_{N}2$ reactions, at the carbon where substitution happens, inversion of configuration occurs because of the concerted nature of the mechanism. Therefore (R)-2-Bromobutane on treatment with $NaI$ in acetone gives (S)-2-iodobutane.