The -OH group is a powerful activating group (+M effect > -I effect) and ortho/para director. Bromination: Phenol + Br2(aq) -> 2,4,6-tribromophenol (white ppt) — no Lewis acid catalyst needed (ring is highly activated). For monosubstitution: use Br2/CS2 at low temperature -> mainly p-bromophenol. Nitration: Dilute HNO3 (298 K) -> mixture of o- and p-nitrophenol (separated by steam distillation — o-isomer is steam-volatile due to intramolecular H-bonding). Conc. HNO3 + conc. H2SO4 -> 2,4,6-trinitrophenol (picric acid). Friedel-Crafts: Does NOT work directly on phenol because -OH coordinates to Lewis acid (AlCl3), deactivating the ring. Workaround: convert -OH to -OCOCH3 (acetyl) first, then FC, then hydrolyse back.