30.1.4—In the electrophilic substitution of arenes,

A substituent changes both the rate and the position of electrophilic substitution on benzene. The syllabus directing set includes –NH₂, –OH, –R, –NO₂, –COOH and –COR.

Electron-donating groups generally direct incoming electrophiles to the 2- and 4-positions; electron-withdrawing groups generally direct to the 3-position. The directing rule predicts mixtures, not one guaranteed product.

Methylbenzene gives mainly 2- and 4-nitro products, while nitrobenzene directs further substitution away from those positions, predominantly to the 3-position.

“Activating” and “directing” are different ideas: a group can slow the reaction yet still direct where substitution occurs.