Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an S_N2 pathway. The reaction in α-haloketones is generally carried out with less basic nucleophiles. The use of strong basic nucleophiles leads to the generation of α-⁠haloenolate ions, which often participate in other side reactions.

However, α-haloacids undergo S_N2 reactions with strong basic nucleophiles. Under this condition, the base abstracts the acidic proton of the acid forming its conjugate base. The anion further participates in a substitution reaction, and the final acidification results in α-substituted acids.

In α-halocarbonyl compounds, nucleophilic substitution via an S_N1 pathway is forbidden, as it generates less stable α-carbocation intermediate.