Question

The electrophilic aromatic substitution proceeds through a:
A. Free radical
B. sigma complex
C. Benzyne
D. Carbene

Answer 1

Hint: Electrophilic aromatic substitution reaction is those in which the electrophile is responsible for the replacement of the atom from the aromatic ring. During the reaction, the formation of the sigma bond takes place.

Complete answer:
-An electrophile is a positively charged particle which can accept the electron pair.
-The action of electrophile is that it makes bonds in the reaction by accepting a pair of electrons from the reacting species.
-In this type of reaction, firstly the electrophile which has a positive charge attack on the $\pi $-bond of the aromatic ring forms carbocation.
-Now, the structure is stabilised with the help of resonance of the single electron that is left.
-Because one after breaking the bond one electron was accepted by the electrophile to make a sigma bond.
-And hence, the formation of the sigma bond takes place.
-The cation formed due to the action of an electrophile is known as sigma complex, named due to the formation of a sigma bond.
-The sigma bond may regain the properties of the aromatic ring by either losing the proton form the benzene ring or by reversing the first step that is the generation of a carbocation.
So, the correct answer is “Option B”.

Note: Free radicals are the atoms of molecules which consist of unpaired valence electrons which are highly reactive and make bonds easily. Whereas benzyne is also a reactive intermediate that is formed in the elimination reaction. A carbene is an electrophile which has two unshared valence electrons.