Question

Arrange in order of decreasing trend towards aromatic electrophilic substitution reaction.
Chlorobenzene (I) , benzene (II) , anilinium chloride (III), toluene (IV).

• A. II > I > III > IV
• B. III > I > II > IV
• C. IV > II > I > III
• D. I > II > III > IV

Answer 1

The correct option is C IV > II > I > III

Aromatic benzene compound undergo electrophilic substitution reaction. The rate of the reaction depends on the substituents present in the benzene ring. $+I$ group in benzene will increase the electron density at ortho and para position and increase the rate of electrophilic substitution reaction. $-I$ group will decrease the rate of electrophilic substitution because it will destabilise the arenium ion formed. Anyhow, $-I$ group are capable of forming meta product.

In the given compound, $C{H}_3$ group in toluene will increase electron density and the molecule will readily undergo electrophilic substitution.
$Cl$ group in chlorobenzene has both $-I$ effect and $+M$ effect. But for halogen group, $-I$ effect is preffered. Hence, it show less reactive toward substitution.

$N{H}_3^{+}$ group is $-I$ effect and it has least ability to undergo substitution.

Benzene is not deactivated by any $-I$ group.
Hence, the order of reactivity toward electrophilic substitution is
$IV>II>I>III$