A Substitution, Nucleophilic, Bimolecular The Sn2 Reaction

R stands for a generic alkyl group. Don t confuse this R with the (R) used to specify one enantiomer of a chiral molecule. This bimolecular reaction is second order overall, which leads to the name Substitution, Nucleophilic, bimolecular, or Sn2 reaction. 

4b Stereochemistry of the Sn2 Reaction One of the most powerful of all tools for investigating the mechanism of a reaction is a stereochemical analysis. In this case, we need first to see what s possible and then to design an experiment 

FIGURE 7.11 One possible stereochemical outcome for the 8 2 reaction. In this scenario, the product is formed with retention of configuration. 

It is also possible that optical activity could be lost. In such a case, (i ) or (S) starting material goes to a racemic mixture—a 50 50 mixture of R) and (5) product (Fig. 7.13). 

FIGURE 7.12 Another possible stereochemical result for the Sn2 reaction. The handedness of the starting material could be reversed in the product, in what is called inversion of configuration. 

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