Final answer:
The reaction of a tosylate with cyanide ion involves a nucleophilic substitution via an SN2 mechanism, resulting in a nitrile product with inverted stereochemistry relative to the starting tosylate.
Step-by-step explanation:
The reaction of a tosylate with a cyanide ion involves a nucleophilic substitution that yields a nitrile product. The cyanide ion, which is a good nucleophile, attacks the electrophilic carbon atom that is attached to the leaving group (in this case, the tosylate). This type of reaction typically proceeds via an SN2 mechanism, where the cyanide ion displaces the tosylate group in a one-step process, where both bond-forming and bond-breaking occur simultaneously.
This SN2 reaction is known for its stereochemical implications. It results in the inversion of configuration at the carbon atom undergoing substitution. Hence, if the starting tosylate had an S stereochemistry, the resulting nitrile will also have an S stereochemistry after the reaction since the attacking nucleophile approaches from the opposite side of the leaving group.
It is important to consider reaction parameters, such as the reaction solvent and temperature, to optimize the yield and selectivity of the desired nitrile product. The presence of a polar aprotic solvent can enhance the nucleophilicity of the cyanide ion and favor the SN2 pathway, thereby ensuring the retention of the desired stereochemistry in the product.