Electrophilic substitution reactions

Aromatic aldehydes and ketones undergo the same broad family of electrophilic AROMATIC substitution reactions that any substituted benzene ring does -- specifically nitration, sulfonation, and halogenation. What is distinctive here is the DIRECTING effect of the carbonyl-bearing group itself: both the aldehydic (-CHO) group and the ketonic (>C=O) group are electron-WITHDRAWING from the ring, acting by both an inductive effect AND a resonance effect together. Because of this combined electron-withdrawal, both groups DEACTIVATE the ring specifically at its ORTHO and PARA positions (pulling electron density away from exactly those two ring positions more than from the meta position), and the net result is that the incoming electrophile in any of these substitutions ends up predominantly at the META position instead -- the exact opposite directing pattern from an electron-donating ring substituent. Worked example: benzaldehyde nitrated with co …