7. why is chlorobenzene less reactive than benzene towards electrophilic substitution reactions ?

Text Solution

more, ortho/paraless, ortho/paramore, metaless meta

Answer : B

Solution : <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/RS_P1_CHM_C19_E01_133_S01.png" width="80%"> <br> <img src="https://d10lpgp6xz60nq.cloudfront.net/physics_images/RS_P1_CHM_C19_E01_133_S02.png" width="80%"> <br> Halogens are unusual in their effect on electrophilic aromatic substitution they are deactivating yet ortho/para directing. Unlike other deactivators, `-I_("effect")` of halogen outweighs its `+R_("effect")` The electron-withdrrawing inductive effect of halogen intensifies the positive charge in arenium ion, makes the ion less stable and causes a slower reaction. due to `+R` effect of halogen, there is an additional resonance structure for ortho and para attack. in this additional resonance structure which is particularly stable, every atom has completed its octet: No such structure is possible for meta attack. Thus, orthopara substitution is relatively faster.