Nucleophilic Substitution Reactions

Nucleophilic substitution is a chemical reaction in which a nucleophile is hungry for positive charge and therefore substitutes itself on a carbon in place of a leaving group.

This reaction can take place using one of two mechanisms:

1. $S_{N}1$, substitution nucleophilic unimolecular, which is a two-step process that includes the formation of a carbocation and nucleophilic attack.
2. $S_{N}2$, substitution nucleophilic bimolecular, which is a one-step process including a concurrent nucleophilic attack on the carbon and the detachment of the leaving group.