Question

The increasing order of reactivity of the following compound towards electrophilic aromatic substitution reaction is:

A. I < III < II
B. II < I < III
C. III < I < II
D. III < II < I

Answer 1

Hint:. Reactivity of electrophilic aromatic substitution is based on many effects; it generally tells us about the stability of the atom out of a number of factors two main factors on which reactivity generally depends are mesomeric and inductive effects.

Complete step by step answer:
Electrophilic aromatic substitution reactions are generally organic reactions in which an electrophile replaces an atom which is attached to an aromatic ring. These reactions involve the replacement of a hydrogen atom belonging to a benzene ring with an electrophile. There are many types of aromatic substitution out of which the most important electrophilic aromatic substitutions are aromatic nitration, aromatic halogenation, aromatic sulfonation, aromatic alkylation and aromatic acylation Friedel–Crafts reaction. The aromaticity of the aromatic system remains as such in an electrophilic aromatic substitution reaction.

The reactivity of the aromatic substitution depends on inductive effect and mesomeric effect like in compound II there is no such type of effect so it is highly reactive as compared to other two. In case of compound I –I effect. –I effect occurs when an electronegative atom like halogen is introduced to a chain of atoms it results in unequal sharing of electrons which generates a positive charge and causes a permanent diploe in the molecule and decreases its reactivity to some lower value. While in compound III –m effect occurs; when the pi-bond electrons are transferred from the conjugate system to a particular group then the electron density of the conjugate system is decreased and then this phenomenon is known as negative mesomeric (–M) effect which decrease the stability of the complex.
So, the correct answer is “Option C”.

Note: By using inductive effect we can predict the acidity and basicity of compounds. It tells us about the electron withdrawing group and electron donating group. electron withdrawing groups increase the acidity of a compound while presence of electron donating groups decrease the basicity of the compound.