In electrophilic aromatic substitution, which substituent directs predominantly to ortho and para positions?

• A. Electron-donating groups (e.g., alkyl, -OH, -OCH3)
• B. Electron-withdrawing groups
• C. Halogens
• D. Meta-directors (e.g., -NO2)

Answer: (A)

In electrophilic aromatic substitution, the directing outcome comes from how a substituent stabilizes the arenium ion intermediate that forms when the ring attacks the electrophile. Electron-donating groups push electron density into the ring and can stabilize the positive charge that appears at the ortho and para positions through resonance. Because those resonance forms place the developing positive charge on the ortho and para carbons, attack at those positions has the lower energy barrier, so substitutions occur predominantly there. Electron-withdrawing groups pull electron density away and destabilize the ortho/para forms, steering the reaction toward meta. Halogens are special in that they can donate electron density by resonance (favoring ortho/para) but are overall deactivating due to inductive withdrawal, so their effect is weaker than strong electron-donating groups. Therefore, the classic directing influence to ortho and para is from electron-donating substituents like alkyl, -OH, or -OCH3.