Aromatic Chemistry

• What are the two major classes of organic chemicals?

  Aliphatic and aromatic (or arenes)
• What distinguishes aromatic hydrocarbons from aliphatic hydrocarbons?

  Aromatic hydrocarbons include one or more rings of six carbon atoms with delocalised bonding
• What is the molecular formula of benzene?

  C6H6
• Describe the basic structure of benzene.

  Benzene has six carbon atoms in a hexagonal ring, with one hydrogen atom bonded to each carbon atom
• How are the carbon atoms in benzene bonded?

  Each carbon atom is bonded to two other carbon atoms and one hydrogen atom by single covalent σ-bonds
• What is the significance of the p orbitals in benzene's structure?

  Each carbon atom has one unused electron in a p orbital, which is perpendicular to the plane of the ring
• What does it mean for the six p electrons in benzene to be delocalised?

  Delocalised means the electrons are not attached to a particular atom but are spread out over the whole ring
• What is the bond angle in benzene?

  120 degrees
• How does the bond length in benzene compare to single and double bonds?

  All C-C bonds in benzene are the same length and have a bond energy between a C-C single bond and a C=C double bond
• What is the difference between the theoretical structure of cyclohexa-1,3,5-triene and actual benzene?

  • Theoretical cyclohexa-1,3,5-triene has 3 double bonds.
  • Actual benzene has delocalised electrons, resulting in less energy release during hydrogenation.
  • Benzene is more thermodynamically stable due to delocalisation.
• What are some examples of aromatic compounds derived from benzene?

  • Methylbenzene
  • Ethylbenzene
  • Chlorobenzene
  • Bromobenzene
  • Nitrobenzene
  • Benzenecarboxylic acid
  • Benzaldehyde
• How are substituents on a benzene ring named when there are two or more present?

  Positions must be indicated by numbers to give the lowest possible numbers, and they are listed in alphabetical order
• What is the phenyl group?

  The C6H5- group that can act as a substituent side group on another molecule
• Why does benzene not generally undergo addition reactions?

  Because addition reactions would involve breaking up the delocalised system
• What type of reactions do benzene typically undergo?

  Benzene typically undergoes electrophilic substitution reactions
• What is the toxicity of benzene?

  Benzene is a carcinogen and is banned for use in schools
• How does methylbenzene differ in toxicity and reactivity compared to benzene?

  Methylbenzene is less toxic and reacts more readily than benzene
• What is the importance of nitration of benzene?

  • It is crucial for synthesising useful compounds.
  • Used in explosive manufacture (e.g., TNT).
  • Formation of amines for dyestuffs.
• What reagents are used in the nitration of benzene?

  Concentrated nitric acid and concentrated sulfuric acid
• What is the mechanism of nitration of benzene?

  The mechanism is electrophilic substitution
• What is the electrophile formed during the nitration of benzene?

  +NO2
• What is the overall equation for the formation of the electrophile in nitration?

  HNO3 + 2H2SO4 → +NO2 + 2HSO4- + H3O+
• What happens to the H+ ion during the nitration reaction?

  The H+ ion rejoins with HSO4- to reform H2SO4 catalyst
• At what temperature is the nitration of benzene typically carried out?

  60 degrees Celsius
• What is Friedel Crafts acylation and its significance?

  • Change in functional group: benzene → phenyl ketone.
  • Reagents: acyl chloride and anhydrous aluminium chloride catalyst.
  • Introduces a reactive functional group onto the benzene ring.
• What is the overall equation for the formation of the electrophile in Friedel Crafts acylation?

  AlCl3 + CH3COCl → [CH3CO]+ + [AlCl4]-
• What happens to the H+ ion during Friedel Crafts acylation?

  The H+ ion reacts with AlCl4- to reform AlCl3 catalyst and HCl
• What is the process of reducing a nitroarene to an aromatic amine?

  • Reagents: Sn and HCl or Fe and HCl.
  • Conditions: Heating.
  • Mechanism: Reduction of nitro group to amine group.
• What is formed when nitrobenzene is reduced?

  Phenylamine
• What is the effect of delocalisation on side groups with lone pairs attached to a benzene ring?

  Delocalisation extends to include the lone pairs, changing the properties and reactions of the side group
• How does delocalisation affect the C-Cl bond in chlorobenzene?

  Delocalisation makes the C-Cl bond stronger and prevents typical substitution reactions
• How does delocalisation affect phenol compared to alcohols?

  Phenol is more acidic and does not oxidise like alcohols
• How does delocalisation affect the basicity of phenylamine compared to aliphatic amines?

  Phenylamine is less basic than aliphatic amines because the lone pair is delocalised and less available for proton acceptance