EDG(2,4 directing) - ring-activating, donate e- to π e^- cloud >

↑ e^- density in ring >

benzene ring > e^--rich, > reactive to electrophilic attack >

requires milder conditions, i.e.

mono-nitration of EDG-mono-subbed arenes, requires temp <30^oC

EWG(1,3 directing) - ring-deactivating, take e^- away from π e^- cloud >

↓ e^- density in ring >

benzene ring < e^--rich, < reactive to electrophilic attack >

requires harsher conditions, i.e.

mono-nitration of EWG-mono-subbed arenes, requires temp >50^oC

Review: H2 Chemistry 13 - Arenes