10 Halogen Derivaties

3. Give reasons

i. Haloarenes are less reactive than halo alkanes.


  • The low reactivity of aryl halides can be attributed to two factors:

    1. Resonance Effect: Aryl halides exhibit low reactivity due to the presence of resonance effects. This effect is a consequence of the π-electron delocalization within the aromatic ring.

    2. sp2 Hybridization: The carbon atom to which the halogen is attached in aryl halides is in a sp2 hybridized state, which further contributes to their low reactivity.

  • In aryl halides, one of the lone pairs of electrons on the halogen atom participates in conjugation with the π-electrons present in the aromatic ring. This resonance interaction plays a crucial role in determining the chemical behavior of these compounds.

  • Due to resonance, the C–X (carbon-halogen) bond in haloarenes acquires partial double bond character, making it stronger and shorter compared to the C–X bond in haloalkanes.

  • For example, the C–Cl bond length in chlorobenzene is 169 pm, while the C–Cl bond length in alkyl chloride is longer at 178 pm.

  • The enhanced bond strength in haloarenes makes it challenging to break the C–X bond in these compounds, leading to their lower reactivity when compared to haloalkanes. This reduced reactivity is a consequence of the stronger and more stable C–X bond in haloarenes.

10 Halogen Derivative Page 232