Arene Chemistry

• What are the two major classes of organic chemicals?

  Aliphatic and aromatic hydrocarbons
• What distinguishes aromatic hydrocarbons from aliphatic ones?

  Aromatic hydrocarbons have one or more rings of carbon
• What is the molecular formula of benzene?

  C6H6
• Describe the basic structure of benzene.

  Six C atoms in a hexagonal ring
• How are the carbon atoms in benzene bonded?

  Each C atom is bonded by single covalent σ-bonds
• What happens to the unused electrons on each carbon atom in benzene?

  They are in p orbitals, perpendicular to the ring
• What is the nature of the six p electrons in benzene?

  They are delocalised in a ring structure
• What is the bond angle in benzene?

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

  It is between a C-C single and C=C double bond
• What does delocalised mean in the context of benzene's electrons?

  Electrons are not attached to a particular atom
• What are the two types of formulas used to represent benzene?

  • Abbreviated formula
  • Displayed formula
• What is the enthalpy change for the hydrogenation of cyclohexene?

  ΔH = -120 kJ/mol
• What is the enthalpy change for the hydrogenation of cyclohexane?

  ΔH = -360 kJ/mol
• What is the enthalpy change for the hydrogenation of benzene?

  ΔH = -208 kJ/mol
• Why is the actual energy of benzene's hydrogenation less than expected?

  Due to delocalisation of the 6 pi electrons
• What is the term for the stability increase due to delocalisation in benzene?

  Delocalisation energy
• What happens in cyclohexa-1,4-diene regarding delocalisation?

  There is no delocalisation due to distance
• How does cyclohexa-1,3-diene compare to cyclohexa-1,4-diene in terms of stability?

  Cyclohexa-1,3-diene has some delocalisation
• How should substituents be numbered on a benzene ring?

  To give the lowest possible numbers
• What is the phenyl group?

  The C6H5- group attached as a substituent
• Why does benzene undergo electrophilic substitution reactions?

  It has high electron density attracting electrophiles
• What is benzene classified as due to its toxicity?

  A carcinogen
• How does methylbenzene's reactivity compare to benzene?

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

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

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

  Electrophilic substitution
• What is the electrophile formed during nitration?

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

  HNO3 + 2H2SO4 → +NO2 + 2HSO4- + H3O+
• What temperature is required for the nitration of benzene?

  60 degrees Celsius
• What is the change in functional group during Friedel Crafts acylation?

  Benzene to phenyl ketone
• What reagents are used in Friedel Crafts acylation?

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

  Electrophilic substitution
• 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 in Friedel Crafts acylation?

  It reacts with AlCl4- to reform AlCl3
• What is the reagent used to reduce nitroarenes to aromatic amines?

  Sn and HCl or Fe and HCl
• What is formed when nitrobenzene is reduced?

  Phenylamine
• What effect does delocalisation have on side groups with lone pairs?

  It extends delocalisation to include lone pairs
• How does delocalisation affect the C-Cl bond in chlorobenzene?

  It makes the C-Cl bond stronger
• How does delocalisation affect phenol compared to alcohols?

  Phenol is more acidic than alcohols
• How does delocalisation affect the basicity of phenylamine?

  It makes phenylamine less basic than aliphatic amines