Nucleophilic Substitution and Elimination

This chapter illustrates two types of nucleophilic substitution: SN1 and SN2 reactions. SN1 is stepwise and unimolecular, proceeding through an intermediate carbocation, with a rate equation of Rate α, that is, proportional only to the concentration of alkyl halide starting material. SN2 is bimolecular with simultaneous bond-making and bond-breaking steps, but does not proceed through an intermediate, with a rate equation of Rate α, that is, the rate is proportional to both the concentration of alkyl halide starting material and the nucleophile. There are important stereochemical consequences of the SN1 and SN2 mechanisms (the former proceeds with racemisation and the latter with inversion). The chapter also describes E1 and E2 eliminations. The Saytzev's Rule and Hofmann's Rule can be used to predict the orientation of elimination, and the stereochemistry is preferentially antiperiplanar.