15.1.3—Nucleophilic substitution

In nucleophilic substitution, a nucleophile donates an electron pair to the carbon attached to X while the C–X bond breaks and X⁻ leaves. Different nucleophiles give different products.

Aqueous OH⁻ gives an alcohol, CN⁻ in ethanol gives a nitrile with one extra carbon, and NH₃ in ethanol gives an amine. AgNO₃ in ethanol can compare halide hydrolysis by precipitating AgX.

CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻; CH₃CH₂Br + CN⁻ → CH₃CH₂CN + Br⁻. The solvent and nucleophile explain the product.

Do not confuse CN⁻ substitution with elimination, and do not forget that the nitrile route increases the carbon count by one.