Question

Give reasons:

Haloarenes are less reactive than haloalkanes.

Answer 1

1. The low reactivity of aryl halides is due to resonance effect and sp2 hybrid state of carbon to which halogen atom is attached.
2. In aryl halides, one of the lone pairs of electrons on halogen atom is in conjugation with π-electrons of the ring. Due to resonance, the C–X bond acquires partial double bond character. Thus, the C–X bond in haloarenes is stronger and shorter than haloalkanes. Hence, it is difficult to break C–X bond in haloarenes. (e.g. C–Cl bond length in chlorobenzene is 169 pm as compared to C–Cl bond length in alkyl chloride which is 178 pm). 

Therefore, haloarenes are less reactive than haloalkanes.