3.3.10.3 Reactivity of Aromatic Compounds

• Benzene consists of a six-carbon ring with each carbon atom bonded to one hydrogen atom
• The π electrons in benzene are confined to individual bonds.

  False
• The six carbon atoms in benzene form a flat, hexagonal structure.

  True
• Delocalization of π electrons in benzene makes it more stable and less reactive.


  True
• Delocalization of π electrons in benzene makes it more reactive than alkenes.

  False
• Order the common reactions of aromatic compounds:

  1️⃣ Nitration

  2️⃣ Halogenation

  3️⃣ Sulfonation

  4️⃣ Friedel-Crafts Alkylation

  5️⃣ Friedel-Crafts Acylation
• Match the reaction with its reagents:

  Nitration ↔️ HNO₃, H₂SO₄

  Halogenation ↔️ Cl₂, FeCl₃

  Sulfonation ↔️ Concentrated H₂SO₄

  Friedel-Crafts Alkylation ↔️ R-X, AlCl₃
• What is the shape of benzene?

  Planar
• What type of electron system does benzene have?

  Delocalized π electrons
• Why is benzene less reactive than alkenes?

  Delocalization of π electrons
• Aromatic compounds undergo electrophilic substitution
• Friedel-Crafts alkylation uses AlCl₃ as a catalyst.


  True
• Match the EAS reaction with its reagents:

  Halogenation ↔️ Cl₂, FeCl₃

  Nitration ↔️ HNO₃, H₂SO₄
• What is the product of sulfonation in EAS?

  Benzenesulfonic acid
• Common electrophilic substitution reactions include nitration, halogenation, sulfonation, and Friedel-Crafts reactions
• What is required to introduce new functional groups in electrophilic substitution reactions?

  Specific reagents and conditions
• Why does electrophilic aromatic substitution preserve the aromatic ring structure?

  Greater stability of aromatic system
• Which type of electron system enhances the stability of aromatic compounds?

  Delocalized π electrons
• Steps in the electrophilic aromatic substitution (EAS) mechanism

  1️⃣ Formation of an electrophilic species

  2️⃣ Electrophilic attack on the aromatic ring

  3️⃣ Wheland intermediate formation

  4️⃣ Deprotonation to give the substituted product
• What does the acronym EAS stand for in chemistry?

  Electrophilic Aromatic Substitution
• Steps in the mechanism of Electrophilic Aromatic Substitution

  1️⃣ Electrophilic Attack

  2️⃣ Wheland Intermediate Formation

  3️⃣ Deprotonation
• Why do aromatic compounds undergo substitution rather than addition reactions in EAS?

  To preserve stability
• In Friedel-Crafts alkylation, the catalyst used is AlCl₃
• In EAS, the electrophile replaces a hydrogen on the aromatic ring.
• The key difference between EAS and alkene addition is that EAS preserves the aromatic ring structure, while alkene addition breaks the double bond.


  True
• Why are alkenes more reactive than aromatic compounds?

  Strained π system
• Which type of substituent increases electron density in an aromatic ring?

  Activating
• Activating substituents direct electrophiles to the ortho- and para- positions.

  True
• Aromatic compounds are generally less reactive than alkenes.
• Unlike cyclohexane, benzene has a planar shape.
• The π electrons in benzene are delocalized
• What type of reaction is characteristic of aromatic compounds like benzene?

  Electrophilic substitution
• In electrophilic aromatic substitution, a Wheland intermediate is formed.
• The delocalized π electrons in benzene stabilize the molecule and make it less reactive.
• Cyclohexane has a planar shape.

  False
• Benzene has equal bond lengths between carbon atoms.

  True
• Arrange the properties of aromatic rings in the correct order:

  1️⃣ Planar shape

  2️⃣ Delocalized π electrons

  3️⃣ Lower reactivity
• Match the reaction with its product:

  Nitration ↔️ Nitrobenzene

  Halogenation ↔️ Chlorobenzene
• Arrange the steps of the EAS mechanism in the correct order:

  1️⃣ Formation of an electrophilic species

  2️⃣ Electrophilic attack on the aromatic ring

  3️⃣ Wheland intermediate formation

  4️⃣ Deprotonation
• EAS preserves the stability of aromatic compounds through delocalization.

  True