JEE MainChemistryGeneral Organic Chemistry
During the electrophilic aromatic substitution of 4-methylphenol ( p -cresol), the incoming electrophile can potentially attack at C₂ (ortho to the -OH group) or at C₃ (ortho to the -CH₃ group). Which of the following statements correctly identifies the major site of attack and the primary electronic reason for this regioselectivity?
Options
- AAttack at C₃ is favored because the +I effect and hyperconjugation of the -CH₃ group outweigh the +M effect of
- BAttack at C₂ is favored because the resulting intermediate forms a highly stable resonance structure where all
- CAttack at C₃ is favored because it produces an intermediate that achieves complete octets for all carbon atoms
- DAttack at C₂ is favored primarily because the -OH group provides less steric hindrance to the incoming electro
Correct answer
B. Attack at C₂ is favored because the resulting intermediate forms a highly stable resonance structure where all
Step-by-step solution
In 4-methylphenol, the -OH group is at C₁ and the -CH₃ group is at C₄ . Both are activating and ortho/para directing groups. When an electrophile attacks at C₂ (ortho to -OH ), the positive charge in the arenium ion intermediate delocalizes to C₁ , C₃ , and C₅ . When the charge is on C₁ , the oxygen atom of the -OH group donates its lone pair to form a C=O -bond. In this specific resonance structure, every atom (except hydrogen) has a complete octet, which provides exceptional stability. When an electrophile attack