JEE Main · 2024 · 01 Feb 2024 · Shift 2 · Hydrocarbons

A substituent directs incoming electrophiles to the meta position when it withdraws electron density from the ring by resonance ($-M$ effect), leaving the ortho and para positions comparatively electron-poor. $-N{O}_2$, $-CHO$, $-S{O}_{3}H$, and $-COR$ are all electron-withdrawing groups with a $-M$ effect through their polarised, electronegative multiple bond conjugated with the ring, so all four are meta directors. The other sets mix in $o$/$p$-directing groups such as $-N{H}_2$, $-NHR$, $-OC{H}_3$, or $-NHCOC{H}_3$, which donate electron density into the ring by resonance.