Why does electrophilic substitution take place at ortho and para positions in haloarenes ?

Explanation

Haloarenes (say chlorobenzene) is a resonance hybrid of following live structures.

Resonance leads to lowering of energy (resonance energy) and hence greater stability. On the other hand, in haloalkanes (say chlorometliane) no such resonance is possible. Thus, we can say that haloareries are more stable than laloalkanes. Halogers directly attached to benzene ring are o, p-directing in electrophilic substitution reactions. This is due to greater electron density at these positions in resonating. Structures II, III and IV. Greater electrons density leads to preferential attack of electrophile on these positions, leading to o-and p-substituted products.