Question

What is the order of reactivity towards electrophilic aromatic substitution of fluorobenzene, chlorobenzene and iodobenzene?

Answer 1

The order of Positive Mesomeric effect `(+M)` effect follows the order `F>Cl>Br>I`

Explanation:

From the order of `+M` effect given above it turns out that the electron density in their respective halobenzene is of order

Fluorobenzene > Chlorobenzene > Iodobenzene

Hence the reactivity towards electrophilic aromatic substitution follows the same order as given above :

Fluorobenzene > Chlorobenzene > Iodobenzene

The relative rates for nitration are given below :-