Question

Nitration of benzene is:
(A) Nucleophilic substitution
(B) Nucleophilic addition
(C) Electrophilic substitution
(D) Free radical substitution

Answer 1

Hint: In this reaction benzene is reacted with concentrated nitric acid and concentrated sulphuric acid. Conc. sulphuric acid being strong donates a proton to nitric acid to form an ion which attaches to the benzene ring.

Complete step by step answer:
-First of all let us see what is meant by nitration of benzene.
A reaction where benzene ($C_6{H}_6$) will react with concentrated nitric acid ($conc.HN{O}_3$) at 323-333K in the presence of concentrated sulphuric acid ($conc.H_{2}S{O}_4$) resulting in the formation of nitrobenzene is known as nitration of benzene.

-We will now talk about the mechanism of this reaction:
 Step-1) The two strong acids: $conc.H_{2}S{O}_4$ and $conc.HN{O}_3$ react with each other to form a very strong electrophile called the nitronium ion. Nitric acid accepts a proton from sulphuric acid because sulphuric acid is a stronger acid.

Step-2) Now benzene will react with this positively charged nitronium ion (electrophile) and leads to the formation of an arenium ion (by breaking one of the N=O bonds).

Step-3) Finally the arenium ion loses a proton to a lewis base (to regain its aromaticity) and leads to the formation of our final product nitrobenzene ($C_6{H}_{5}N{O}_2$).

Here we can see that we have replaced a hydrogen atom from the benzene ring with a strong electrophile (nitronium ion, $N{O}_2^{+}$), and hence we can call nitration of benzene as an electrophilic substitution reaction.
So, the correct answer is “Option C”.

Note: An electrophile is an ion which is itself positively charged and gets attracted to electron rich atoms or molecules, while a nucleophile is an ion which itself is negatively charged and gets attracted to electron deficient atoms or compounds. So, in an electrophilic substitution reaction an electrophile replaces another electrophile.