A chemist needs to synthesize (S)-2-cyanobutane from enantiomerically pure (R)-2-iodobutane. To achieve the highest possible enantiomeric excess of the desired product, which of the following sets of reagents and solvent conditions is the most appropriate?

Step-by-step solution

To convert (R)-2-iodobutane to (S)-2-cyanobutane with the highest enantiomeric excess, the reaction must proceed with complete inversion of configuration. This requires forcing the secondary alkyl halide strictly through an S _ N 2 pathway, avoiding any S _ N 1 mechanism which would lead to racemization. An S _ N 2 mechanism is favoured by a high concentration of a strong nucleophile in a polar aprotic solvent. Using KCN provides the strong nucleophile CN ⁻ . DMF is a polar aprotic solvent, which enhances the nucle