Aromatics

• Aromatic Hydrocarbons


  Circularly structured organic compounds that contain sigma bonds along with delocalized pi electrons
• Aromatic Compounds


  • Originally named because of their fragrant properties
  • Unsaturated hydrocarbon ring structures that exhibit special properties, including unusual stability, due to their aromaticity
  • Often represented as resonance structures containing single and double bonds
  • Bonding is stronger than expected for a conjugated structure, and it is more accurately depicted as delocalized electron density shared between all the atoms in the ring
• Benzene Ring


  • Benzene can only be fully depicted with all of its resonance structures, which show how its pi-electrons are delocalized throughout its six-carbon ring
  • This delocalization leads to a lower energy for the molecule, giving it greater stability
• Aromatic compounds are produced from a variety of sources, including petroleum and coal tar
• Poly-aromatic hydrocarbons are components of atmospheric pollution and are known carcinogens
• Aromatic compounds are also interesting because of their presumed role in the origin of life as precursors to nucleotides and amino acids
• Aromatic Hydrocarbons


  • Exhibit aromaticity (additional stability granted by resonance)
  • The ratio of carbon atoms to hydrogen atoms is relatively high
  • When burnt, they display a strong and sooty flame which is yellow
  • They generally undergo electrophilic substitutions and nucleophilic aromatic substitution reactions
• Uses of Aromatic Hydrocarbons

  • Green pigment found in plants (chlorophyll)
  • Nucleic acids and amino acids in the human body
  • Methylbenzene used as a solvent in model glues
  • Naphthalene in mothball production
  • Phenanthrene used for synthesis of drugs, dyes, and explosives
  • Trinitrotoluene (TNT) used for explosive purposes
  • Plastic industry and petrochemical industries
• Polycyclic Aromatic Hydrocarbons


  • Hydrocarbons which comprise of aromatic rings in fused form
  • Found in coal, tar, oil and some cooked foods such as smoked fish, burnt toast
• Aromatic Hydrocarbons


  • Methylbenzene
  • Naphthalene
  • Phenanthrene
  • Trinitrotoluene
  • o-dihydroxybenzene
• Some aromatic compounds, benzene among them, are toxic
• The compound 1,2-benzopyrene was the cause of the first demonstrated case of occupational disease which is cancer
• Benzopyrene is a component of pitch and occurs together with other related pentacyclic aromatic species such as picene, benzofluoranthenes, and perylene
• Benzopyrene is naturally emitted by forest fires and volcanic eruptions and can also be found in coal tar, cigarette smoke, wood smoke, and burnt foods such as coffee
• Fumes that develop from fat dripping on blistering charcoal are rich in benzopyrene, which can condense on grilled goods
• Phenyl group


  C6H5, a benzene ring minus a hydrogen atom
• Benzyl group


  Ar-, an aryl group (any aromatic ring)
• Cases where the name is based on phenyl

  • Phenylamine (aniline, aminobenzene)
  • Phenylethene (styrene)
  • Phenylethanone
• Benzene Nomenclature in Organic Chemistry by Knowbee
• Naming Aromatic Compounds Benzene and Phenyl in Organic Chemistry
• Google classroom, Google meet, module