Question

The decreasing order of reactivity towards electrophilic substitution reaction of the following compounds is:
i.Benzene
ii.Chlorobenzene
iii.Nitrobenzene
iv.Toluene
A.i > iii > iv > ii
B.iv > i > iii > ii
C.iv > i > ii > iii
D.iv > ii > i > iii

Answer 1

Hint: For an electrophilic aromatic substitution reaction, we should know that the existing substituent groups attached to the aromatic ring have the ability to influence the rate of an overall reaction. These groups can be either electron donating or electron withdrawing.

Complete step by step answer:
-Generally, there are two types of groups - activating and deactivating groups. Activating group is any substituent which increases the reactivity of the organic compound whereas a deactivating group tends to decrease the reactivity of the organic compound.
-The activating group directs the reaction to the ortho and para positions of the aromatic benzene ring whereas the deactivating group directs the reaction to the meta position of the ring.
-Electrophilic aromatic substitution reaction rate increases when benzene is attached to the deactivating group which is also known as electron withdrawing group. But the reaction rate decreases if the benzene is attached to the activating group, also called the electron donating group.
-For example, the reactivity of phenol is more because the methyl group present on the methoxy substituent makes the oxygen less activating or donating in nature. Generally, strong activating groups are aniline, phenol; moderately activating groups such as acetanilide and weakly activating are alkyl benzene, diphenyl and vinyl benzene. Strong deactivating groups are benzene, nitrobenzene; moderately deactivating groups are benzaldehyde, acetophenone and weakly deactivating group is chlorobenzene.
-Using this information, we can determine the general order of reactivity as: aniline > phenol > anisole > acetanilide > toluene > chlorobenzene > benzoic acid > nitrobenzene.
Therefore, the correct order of reactivity towards electrophilic substitution reaction is toluene > benzene > chlorobenzene > nitrobenzene.

Hence, the correct option is (C).
Note:
We should know that electrophile is an electron deficient species and therefore the one which is most reactive toward an electrophilic attack will be definitely an electron rich species. So, we can say that in these reactions, an electrophile attacks on the nucleophilic substrate. If the incoming group is bulky it generally attaches to the para position specifically to avoid steric hindrance.