Question

The Cl atom in chlorobenzene is ortho and
para directing and weakly ring deactivating
group. Give reason.

Answer 1

Answer:

The -I effect of chlorine withdraws electron from Benzene ring. Hence tends to destabilize the intermediate carbocation formed during Electrophilic substitution. Conversely, Cl donates it's lone pair electron to the aromatic ring and hence increase the electron density at Ortho and para positions. Thus the lone pair of an electron on chlorine atom stabilize the intermediate carbocation due to resonance.

Since -I effect of Chlorine is stronger than it's +R effect hence Cl cause net deactivation. Also further since Resonance effect opposes the inductive effect, it makes deactivation less at Ortho and para positions.

Thus in Chlorobenzene, reactivity is controlled by stronger -I effect while the orientation of incoming substituent group is controlled by a weaker resonance effect

Explanation:

hope you understand