Aromatic chemistry

• What are the two major classes of organic chemicals?

  Aliphatic and aromatic (arenes)
• What defines aromatic hydrocarbons or arenes?

  Includes one or more rings of six carbons
• 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 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 C-C single and C=C double bonds?

  It is between the lengths of both bonds
• What does delocalised mean in the context of benzene?

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

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

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

  ΔH = -208 kJ/mol
• What is the theoretical enthalpy change for cyclohexa-1,3,5-triene?

  ΔH = -360 kJ/mol
• What is the actual enthalpy change for benzene compared to the theoretical value?

  It is less than the theoretical value
• What is the term for the increase in stability due to delocalisation in benzene?

  Delocalisation energy
• Why does cyclohexa-1,4-diene not exhibit delocalisation?

  Pi electrons are too far apart to overlap
• What is the hydrogenation value for cyclohexa-1,4-diene?

  -240 kJ/mol
• What is the hydrogenation value for cyclohexa-1,3-diene?

  Less negative than -240 kJ/mol
• What are the naming conventions for aromatic compounds?

  • Use benzene as the root name
  • Indicate positions with numbers
  • List substituents in alphabetical order
  • Use di, tri prefixes for multiple substituents
• What is the name of the compound with a methyl group attached to benzene?

  Methylbenzene
• What is the name of the compound with a nitro group attached to benzene?

  Nitrobenzene
• What is the name of the compound with a carboxylic acid group attached to benzene?

  Benzenecarboxylic acid
• How are substituents 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 not undergo addition reactions?

  It would break the delocalised system
• What type of reactions does benzene typically undergo?

  Electrophilic substitutions
• What is the toxicity of benzene?

  Benzene is a carcinogen
• How does methylbenzene's toxicity compare to benzene?

  Methylbenzene is less toxic than benzene
• What is the importance of nitration of benzene?

  It synthesizes useful compounds like explosives
• What reagents are 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 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 temperature is used for the nitration of benzene?

  60 degrees Celsius
• What happens at higher temperatures during nitration?

  A second nitro group can be substituted
• What is the mechanism for the formation of the electrophile in nitration?

  1. HNO3 acts as a base
  2. Accepts a proton from sulfuric acid
  3. Intermediate loses a water molecule
  4. Electrophile +NO2 is formed
• 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 conditions are required for Friedel Crafts acylation?

  Heat under reflux at 50 degrees Celsius