What is Substitution reaction?

A substitution reaction is a chemical process where one functional group in a molecule is replaced by another. This type of reaction is prevalent in organic chemistry and can be categorized mainly into nucleophilic substitution and electrophilic substitution. In nucleophilic substitution, an electron-rich nucleophile replaces a leaving group, with mechanisms like S_N1, which involves a two-step process forming a carbocation intermediate, and S_N2, a single-step process where the nucleophile directly displaces the leaving group. Electrophilic substitution, common in aromatic compounds, involves an electron-poor electrophile replacing a group on the aromatic ring.