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Electrophilic Aromatic Substitution (EAS) involves directing effects of substituents on the aromatic ring:

Strongly Activating Groups

• Definition: Increase electron density; reactive towards electrophiles.

• Examples: Amines, Alcohols, Ethers.

• Mechanism: Donate electrons via resonance, primarily directing substitution to ortho-para positions.

Moderately Activating Groups

• Definition: Increase electron density but less effectively.

• Examples: Amides, Esters.

• Mechanism: Can donate electron density but less effectively, still ortho-para directors.

Weakly Activating Groups

• Definition: Minimal density effect; donate via sigma bond.

• Examples: Alkyl Groups.

• Mechanism: Directs substitution to ortho and para due to more stable carbocations.

Weakly Deactivating Groups

• Definition: Slightly reduce electron density.

• Examples: Halogens.

• Mechanism: Dual role of withdrawing and donating via resonance; still ortho-para directors.

Moderately Deactivating Groups

• Definition: Withdraw electron density, acting as meta directors.

• Examples: Aldehydes, Ketones, Carboxylic Acids.

• Mechanism: Engage in resonance withdrawal, directing attacks away from ortho-para positions.

Strongly Deactivating Groups

• Definition: Effectively withdraw electron density.

• Examples: Nitro Group, Cyanide, Sulfonic Acid.

• Mechanism: Direct substitution to meta position due to destabilization of ortho and para.

Summary

Understanding the reactivity and directing effects of substituents is crucial for predicting outcomes in synthetic organic chemistry, activating or deactivating the aromatic ring and influencing electrophilic attack positions.