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.