Aromatic Chemistry

• What is the study of benzene and compounds containing the benzene ring called?

  Aromatic chemistry
• Benzene compounds are known as arenes
• What is the simplest aromatic hydrocarbon?

  Benzene
• Benzene was first isolated in 1825.
• What is the empirical formula of benzene based on its percentage composition?

  CH
• The molecular formula of benzene is C₆H₆
• Friedrich August Kekulé proposed a structure for benzene in 1865.
• Match the evidence against the Kekulé structure with the corresponding explanation:

  Benzene does not decolourise bromine water ↔️ If benzene contained C=C, it would react with bromine water

  Equal carbon-carbon bond lengths ↔️ C=C bonds are shorter than C-C bonds, but benzene has 6 equal bonds
• The hydrogenation of benzene is less exothermic than expected for the Kekulé structure.
• The delocalisation energy of benzene is 152 kJ/mol.
• What is the shape of the benzene molecule?

  Planar
• Electrons in the π-bond of benzene are delocalised.
• What is the enthalpy change for the hydrogenation of cyclohexene?

  -120 kJ/mol
• The π-bond in cyclohexene arises from the overlap of adjacent p-orbitals.
• Which diene, cyclohexa-1,3-diene or cyclohexa-1,4-diene, has the least exothermic enthalpy of hydrogenation?

  Cyclohexa-1,3-diene
• Match the structural isomers of C8H10 with their names:

  1,2-dimethylbenzene ↔️ CH3 group at positions 1 and 2

  1,3-dimethylbenzene ↔️ CH3 group at positions 1 and 3

  1,4-dimethylbenzene ↔️ CH3 group at positions 1 and 4

  Ethyl benzene ↔️ C2H5 group attached to benzene
• What type of reaction occurs when benzene reacts with electrophiles?

  Electrophilic substitution
• Sulfuric acid acts as a catalyst in the nitration of benzene.
• Outline the mechanism for the nitration of benzene.

  1️⃣ Generation of the nitronium ion (NO₂⁺)

  2️⃣ Formation of organic product

  3️⃣ Regeneration of the sulfuric acid catalyst
• What type of reaction is Friedel-Crafts acylation?

  Electrophilic substitution
• What is the product formed when benzene reacts with methyl chloride in the presence of AlCl₃?

  Methylbenzene
• Benzene reacts with bromine in the same way as cyclohexene.

  False
• The methyl group in methylbenzene releases electrons, increasing the electron density of the ring.
• What reagents are used to reduce a nitro group to an amine?

  Tin and concentrated HCl