(S)-1-Bromo-2-methylbutane, BrCH2-CH(CH3)-CH2CH3, reacts with KCN in DMSO (SN2 at the CH2Br carbon). The product 3-methylpentanenitrile is

achiral, because the stereocentre is lost

JEE Main levelSingle correct optionDifficulty 2 of 3hx211

(S)-1-Bromo-2-methylbutane, $BrCH X_{2} - CH (CH X_{3}) - CH X_{2} CH X_{3}$ , reacts with $KCN$ in DMSO (SN2 at the $CH X_{2} Br$ carbon). The product 3-methylpentanenitrile is

The stereocentre is not the reacting carbon, so none of its bonds is broken and the spatial arrangement is retained. Priorities:

CH X_{2} Br

C X_{2} H X_{5}

CH X_{3}

> H in the substrate and

CH X_{2} CN

C X_{2} H X_{5}

CH X_{3}

> H in the product, so the label stays S.