Question

Why do alkyl halides show nucleophilic substitution reactions?

Why do alkyl halides undergo nucleophilic substitution reactions?

Answer 1

1. In alkyl halides (R–X), the carbon–halogen (C–X) bond is polar because halogen is more electronegative than carbon.
2. This makes the carbon atom electron-deficient (δ⁺) and the halogen atom electron-rich (δ⁻).
3. The electron-deficient carbon atom acts as an electrophilic centre.
4. Nucleophiles (electron-rich species) are attracted by this partially positive carbon.
5. At the same time, the halide ion (X⁻) is a good leaving group because it is stable after departure.
6. For example, The C–Cl bond in ethyl chloride is polar. Carbon is electron-deficient (δ⁺), so it is attacked by the nucleophile OH⁻. The Cl⁻ ion leaves as a stable leaving group, and the –OH group replaces –Cl, forming ethyl alcohol (CH₃CH₂OH).
   \[\ce{CH3 - CH2 - Cl + OH^-  -> CH3 - CH2 - OH + Cl^-}\]

Hence, alkyl halides undergo nucleophilic substitution reactions, where the halogen atom is replaced by a nucleophile.