Aromatic compound's and amines

• 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?

  It means the electrons are spread out over the whole ring and not attached to a particular atom
• 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, leading to lower energy.
  • Delocalisation makes benzene more thermodynamically stable.
• What is the delocalisation energy in benzene?

  It is the increase in stability connected to delocalisation
• Why does cyclohexa-1,4-diene not exhibit delocalisation?

  Because the pi electrons are too far apart and do not overlap
• What happens to the hydrogenation value in cyclohexa-1,3-diene?

  It would be less negative than -240 kJ/mol, indicating more stability
• How are aromatic compounds named when multiple substituents are present?

  • Use numbers to indicate positions for lowest possible numbers.
  • List different substituents in alphabetical order.
  • Use di, tri prefixes for multiple identical substituents.
• What is the phenyl group?

  The C6H5- group that acts as a substituent side group
• Why does benzene not generally undergo addition reactions?

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

  Electrophilic substitutions
• Why is benzene considered a carcinogen?

  Because it is a cancer-causing molecule
• How does methylbenzene differ from benzene in terms of toxicity and reactivity?

  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).
  • Forms amines for dye production.
• What are the reagents used in the nitration of benzene?

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

  Electrophilic substitution
• What is the electrophile in 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 after the nitration reaction?

  It rejoins with HSO4- to reform H2SO4 catalyst
• At what temperature is the nitration of benzene typically performed?

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

  • Change in functional group: benzene → phenyl ketone.
  • Uses acyl chloride and anhydrous aluminium chloride.
  • Introduces a reactive functional group onto the benzene ring.
• What is the reagent used in Friedel Crafts acylation?

  Acyl chloride in the presence of anhydrous aluminium chloride
• What is the mechanism of Friedel Crafts acylation?

  Electrophilic substitution
• What is formed during the reaction of acyl chloride with aluminium chloride?

  The electrophile RCO+
• What happens to the H+ ion after Friedel Crafts acylation?

  It reacts with AlCl4- to reform AlCl3 catalyst and HCl
• What is the process of reducing a nitroarene to aromatic amines?

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

  Phenylamine
• What happens to the ionic salt formed during the reduction of nitroarene?

  It is soluble in water and can react with NaOH to give insoluble phenylamine
• How does delocalisation affect side groups with lone pairs attached to benzene?

  • Delocalisation extends to include lone pairs on N, O, and Cl.
  • Changes properties and reactions of the side group.
  • Strengthens C-Cl bond and weakens O-H bond in phenol.
• How does the presence of a –OH group affect phenol compared to alcohols?

  Phenol is more acidic and does not oxidise like alcohols
• How does the delocalisation of the lone pair in phenylamine affect its basicity?

  It makes phenylamine less basic than aliphatic amines
• What should students remember about questions regarding aromatic compounds?

  • Many questions will focus on aliphatic reactions of side chains.
  • Not all questions will be about the benzene ring itself.
• What type of compound is benzene?

  Aromatic compound
• How many carbon atoms are in benzene?

  Six carbon atoms