aromatic hydrocarbon

Examples of aromatic hydrocarbon in the following topics:

• Introduction to Hydrocarbons

  • This class can be further divided into two groups: aliphatic hydrocarbons and aromatic hydrocarbons.
  • Aromatic hydrocarbons, or arenes, which contain a benzene ring, were originally named for their pleasant odors.
  • For example, a chemical structure can be both aromatic and contain an alkyne.
  • The study of hydrocarbons is particularly important to the fields of chemical and petroleum engineering, as a variety of hydrocarbons can be found in crude oil.
  • The benzene molecules and its derivatives are the basis for aromatic structures.

• Properties of Aromatic Compounds

  • Aromatic compounds, originally named because of their fragrant properties, are unsaturated hydrocarbon ring structures that exhibit special properties, including unusual stability, due to their aromaticity.
  • Aromatic compounds are generally nonpolar and immiscible with water.
  • This stability is lost in electrophilic addition because the product is not aromatic.
  • 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.

• Other Aromatic Compounds

  • Benzene is the archetypical aromatic compound.
  • Four illustrative examples of aromatic compounds are shown above.
  • The first example is azulene, a blue-colored 10 π-electron aromatic hydrocarbon isomeric with naphthalene.
  • Remarkably, this hydrocarbon is chemically unstable, in contrast to most other aromatic hydrocarbons.
  • Formulation of the Hückel rule prompted organic chemists to consider the possible aromaticity of many unusual unsaturated hydrocarbons.

• Antiaromaticity

  • Conjugated ring systems having 4n π-electrons (e.g. 4, 8, 12 etc. electrons) not only fail to show any aromatic properties, but appear to be less stable and more reactive than expected.
  • Examples of 8 and 12-π-electron systems are shown below, together with a similar 10 π-electron aromatic compound.
  • The simple C8H6 hydrocarbon pentalene does not exist as a stable compound, and its hexaphenyl derivative is air sensitive.
  • On the other hand, azulene is a stable 10-π-electron hydrocarbon that incorporates structural features of both pentalene and heptalene.
  • Azulene is a stable blue crystalline solid that undergoes a number of typical aromatic substitution reactions.

• Substitution Reactions of Benzene and Other Aromatic Compounds

  • The remarkable stability of the unsaturated hydrocarbon benzene has been discussed in an earlier section.
  • Since the reagents and conditions employed in these reactions are electrophilic, these reactions are commonly referred to as Electrophilic Aromatic Substitution.

• Reactions of Fused Benzene Rings

  • Compounds in which two or more benzene rings are fused together were described in an earlier section, and they present interesting insights into aromaticity and reactivity.
  • The smallest such hydrocarbon is naphthalene.

• Benzene and other Aromatic Compounds

  • The adjective "aromatic" is used by organic chemists in a rather different way than it is normally applied.
  • Benzoic acid was eventually converted to the stable hydrocarbon benzene, C6H6, which also proved unreactive to common double bond transformations, as shown below.
  • As experimental evidence for a wide assortment of compounds was acquired, those incorporating this exceptionally stable six-carbon core came to be called "aromatic".
  • This sort of stability enhancement is now accepted as a characteristic of all aromatic compounds.
  • A molecular orbital description of benzene provides a more satisfying and more general treatment of "aromaticity".

• Directed ortho-Metalation

  • Among the most useful reactions for the synthesis of complex molecules are those that achieve direct selective functionalization of a hydrocarbon moiety.
  • Snieckus (University of Waterloo, Ontario, Canada) the ortho-lithiation of functionally substituted aromatic rings has proven to be a powerful technique for regioselective synthesis.
  • Electrophilic substitution of aromatic rings generally gives a mixture of ortho and para substitution products when an existing substituent activates the ring or meta products when the substituent is deactivating.

• Reactions of Aromatic Compounds

  • An example of an aromatic substitution reaction is shown below.
  • In a nucleophilic aromatic substitution reaction, a nucleophile displaces a substituent on an aromatic ring.
  • In an electrophilic aromatic substitution reaction, a substituent on an aromatic ring is displaced by an electrophile.
  • These reactions include aromatic nitration, aromatic halogenation, aromatic sulfonation, and Friedel-Crafts acylations and alkylations.
  • Example of an aromatic substitution reaction.

• Alkanes

  • Hydrocarbons having no double or triple bond functional groups are classified as alkanes or cycloalkanes, depending on whether the carbon atoms of the molecule are arranged only in chains or also in rings.
  • Although these hydrocarbons have no functional groups, they constitute the framework on which functional groups are located in other classes of compounds, and provide an ideal starting point for studying and naming organic compounds.
  • Simply put, aliphatic compounds are compounds that do not incorporate any aromatic rings in their molecular structure.
  • This is also the highest possible H/C ratio for a stable hydrocarbon.