How do aromatic aldehydes and ketones react in electrophilic substitution, and what role does the carbonyl group play in directing the substitution on the aromatic ring?

Aromatic aldehydes and ketones undergo electrophilic substitution reactions on the aromatic ring. The carbonyl group, when present, directs the substitution by activating the ortho and para positions toward electrophilic attack due to resonance effects. The π electrons of the aromatic ring can delocalize onto the carbonyl oxygen, creating a partial positive charge on the ortho and para positions. This enhances the nucleophilic nature of these positions, making them more susceptible to electrophilic substitution. This directing effect is known as the carbonyl group’s ortho-para directing influence and influences the regiochemistry of the substitution reactions on the aromatic ring.