Question

The major product obtained in the following reaction is Chlorobenzene + chlorine $\xrightarrow{\text{Anhydrous }\text{FeCl}_3}$ product (Major)

• A. 1, 3, 5-trichlorobenzene
• B. 1, 4-dichlorobenzene
• C. 1, 2-dichlorobenzene
• D. 1, 3-dichlorobenzene

Hint:

For almost all ortho/para-directing substitutions on monosubstituted benzene rings, the para-product is structurally favored as the major product due to minimized steric clash.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks for the major organic product formed when chlorobenzene undergoes electrophilic aromatic substitution (halogenation) with chlorine gas in the presence of a Lewis acid catalyst ($\text{FeCl}_3$).

Step 2: Key Formula or Approach:
The chlorine atom already attached to the benzene ring has lone pairs of electrons that can be delocalized into the ring via resonance ($+R$ effect), making it an ortho/para-directing group.

Step 3: Detailed Explanation:
The resonance effect increases electron density specifically at the ortho and para positions of the chlorobenzene ring. Electrophilic attack by the chloronium ion ($\text{Cl}^+$) occurs at these sites, yielding a mixture of 1,2-dichlorobenzene (ortho-product) and 1,4-dichlorobenzene (para-product).
Between these two, the para-isomer (1,4-dichlorobenzene) is the major product because it experiences significantly less steric hindrance compared to the crowded ortho-isomer. Additionally, the symmetrical nature of the para-isomer offers greater structural stability.

Step 4: Final Answer:
The major product of the chlorination of chlorobenzene is 1,4-dichlorobenzene, which corresponds to option (B).