16 Chapter Electrophilic Aromatic Substitution

Electrophilic Aromatic Substitution Reactions (EAS)

FAR

1) Form Electrophile

2) Attack Electrophile:

3) Restore Aromaticity

1) Chlorination

• Cl2

• AlCl3

1) Bromination

• Br2

• FeBr3

Benzene → Halogenation

1) Form Electrophile: X2 and Al/FeX3 bind

2) Attack Electrophile: 3 Resonance Structures Form

3) Restore Aromaticity: H is deprotonated by extra X to form Aryl Halogen, H-X, and MetalX3

2) SO3, H2SO4

Benzene → Sulfonation

1) Form Electrophile

2) Attack Electrophile:

3) Restore Aromaticity

REVERSIBLE

3) R-OH, H2SO4

Benzene → Alkylation

1) Form Electrophile

2) Attack Electrophile:

3) Restore Aromaticity

4) HNO3, H2SO4

Benzene → Nitration

1) Form Electrophile

2) Attack Electrophile:

3) Restore Aromaticity

5) R-Cl, AlCl3

Benzene → Friedel-Crafts- Alkylation

IMPORTANT INFO:

1) BEWARE of Carbocation Rearrangements

2) METHYL and Ethyl Halides React using SN2

3) Multiple Alkylations are Typical

4) Source of Carbocation can come from

• Cl substituent + AlCl3 (Flaschard 5 (THIS))

• Carbocation + H2SO4

• OH substituent + H2SO4 (Flashcard 3)

**1) BEWARE OF CARBOCATION REARRANGEMENTS

If it’s a 1° Carbocation, performa 1-2 Hydride shift to create a 3° Carbocation

**2) METHYL and Ethyl Halides React using SN2

CH3-Br

CH3-CH2-Br

**SAME FORMAT Mechanism as the Halogenation EAS Mechanism, But just SN2

6) Acid Chloride, AlCl3

Benzene → Friedel-Crafts- Acylation

-NO Multiple Alkylations

-This is because C double bond O is an EWG and DEACTIVATING group