Step 1: Identifying the transformation. 4-Methylphenol treated with CHCl₃ and NaOH undergoes the Reimer–Tiemann reaction, introducing a formyl (–CHO) group onto the aromatic ring. Step 2: Phenoxide activation. NaOH deprotonates phenol to phenoxide, powerfully activating the ring for electrophilic attack at ortho and para positions. Step 3: Electrophile generation. Chloroform in basic medium produces dichlorocarbene (:CCl₂), which serves as the electrophilic species. Step 4: Directing influences. Both –OH and –CH₃ are ortho/para directors; however, steric factors favor reaction at the less hindered para position relative to –OH. Step 5: Major product. The formyl group predominantly enters para to the hydroxyl, affording a p-hydroxybenzaldehyde derivative. Step 6: Conclusion. The major product is a para-substituted hydroxybenzaldehyde.
