In electrophilic aromatic substitution reaction of chlorobenzene, the ortho/para directing ability of chlorine is due to which of the following effects?

• A. Positive Inductive Effect (+I)
• B. Negative Inductive Effect (-I)
• C. Positive Resonance Effect (+R)
• D. Negative Resonance Effect (-R)

In the electrophilic aromatic substitution reaction of chlorobenzene, the ortho/para directing ability of chlorine is primarily due to its positive resonance effect (+R). This effect allows chlorine to donate electron density to the aromatic ring through resonance, stabilizing the carbocation intermediate formed during the reaction. As a result, electrophiles are more likely to attack at the ortho and para positions.

Key Concepts

• Positive Resonance Effect (+R): Chlorine can donate electron density, enhancing reactivity at certain positions.
• Ortho/Para Directing: The presence of chlorine leads to preferential substitution at the ortho and para sites.

Other Effects Explained

While chlorine also exhibits a negative inductive effect (-I), which withdraws electron density, its resonance effect is stronger and dominates in this context. Thus, the correct answer is:

C. Positive Resonance Effect (+R)