Question

Account for the following:

Haloalkanes undergo nucleophilic substitution reactions.

Answer 1

1. Haloalkanes undergo nucleophilic substitution reactions due to the nature of the carbon-halogen (C–X) bond, where the halogen (X) is electronegative and creates a polar bond. This polarity makes the carbon atom electrophilic (electron-deficient) and thus susceptible to attack by nucleophiles (electron-rich species).
2. In nucleophilic substitution reactions, the nucleophile attacks the electrophilic carbon attached to the halogen, leading to the displacement of the halogen atom.
3. The reaction can follow either the ( S_N1 ) or ( S_N2 ) mechanism, depending on the nature of the haloalkane (primary, secondary, or tertiary):
   • (S_N2) Mechanism: Occurs mainly with primary haloalkanes. The nucleophile attacks the carbon from the opposite side of the leaving group in a single step, leading to inversion of configuration.
   • (S_N1) Mechanism: Common with tertiary haloalkanes. It involves two steps first, the departure of the halide ion to form a carbocation intermediate, followed by nucleophilic attack on the carbocation.
4. Haloalkanes react with various nucleophiles such as hydroxide ions (to form alcohols), cyanide ions, ammonia, and amines, among others. The nucleophiles replace the halogen atom in the molecule.