Substituent Effects in Electrophilic Aromatic Substitution
Start with the big picture
Substituents affect EAS through a balance of resonance (±M) and inductive (±I) effects on electron density and σ-complex stability. Electron-donating groups such as −NH₂, −OH, −OR, −NHCOR, and alkyl groups generally activate the ring and direct substitution to ortho and para positions. Electron-withdrawing groups such as −NO₂, −CF₃, −CN, −SO₃H, and carbonyl groups generally deactivate the ring and direct substitution to meta positions. Halogens are a key exception: they deactivate by induction but direct ortho/para through resonance. Steric bulk can favor para over ortho, while rings with multiple substituents reflect competing directing effects. The full lesson also considers Friedel–Crafts limitations and relative reactivity trends.
What you'll learn
- Explain how resonance and induction affect σ-complex stability in EAS.
- Classify common substituents as activating or deactivating and identify their directing tendencies.
- Explain why halogens deactivate rings yet direct ortho/para substitution.
- Describe how steric bulk and multiple substituents influence product orientation.
- Recognize ring conditions that limit Friedel–Crafts reactions.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
