The SN2 reaction of (S)-(–)-2-bromobutane will proceed with:

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Correct Answer: D. inversion of configuration.
A quick SN2 reminder: The SN2 reaction is a single-step displacement of a leaving group by a nucleophile. During the transition state, the bond to the nucleophile forms at the same time that the bond to the leaving group breaks. Thus, the nucleophile needs to approach from the back, and configuration at carbon is inverted. Not only is inversion possible, it is inevitable. Inversion of the configuration always occurs in SN2 reactions. The backside attack of the nucleophile causes the inversion. Therefore if a pure enantiomer reactant is used, then the product has the opposite absolute configuration.
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