Question

How does chlorine substitution on a phenyl ring modify the reactivity of the ring?

Answer 1

Because the electronegative chlorine atom withdraws electron density from the ring, making the ring less nucleophilic.

Explanation:

So, by induction, the chloro-substituted phenyl ring is a less powerful nucleophile, and thus, less likely to undergo substitution by electrophiles. Because of the lone pairs on the chloride, it is an `"ortho"` and `"para"` director in those reactions where it does undergo substitution.