Polycyclic aromatic hydrocarbons

(noun)

also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents.

Related Terms

  • carcinogenic
  • mutagenic

Examples of Polycyclic aromatic hydrocarbons in the following topics:

  • Polycyclic Aromatic Hydrocarbons

    • Polycyclic aromatic hydrocarbons are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms.
    • It can degrade high molecular mass polycyclic aromatic hydrocarbons of 4 and 5 rings.
    • Polycyclic aromatic hydrocarbons (PAHs), also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are seen in .
    • It can degrade high molecular mass polycyclic aromatic hydrocarbons of 4 and 5 rings.
    • An image showing three examples of polycyclic aromatic hydrocarbons.
  • 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.
  • Anoxic Hydrocarbon Oxidation

    • Anoxic hydrocarbon oxidation can be used to degrade toxic hydrocarbons, such as crude oil, in anaerobic environments.
    • Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon.
    • Crude oil contains aromatic compounds that are toxic to most forms of life.
    • Although it was once thought that hydrocarbon compounds could only be degraded in the presence of oxygen, the discovery of anaerobic hydrocarbon-degrading bacteria and pathways show that the anaerobic degradation of hydrocarbons occurs naturally.
    • Microbes may be used to degrade toxic hydrocarbons in anaerobic environments.
  • Hydrocarbons

    • Hydrocarbons are organic molecules consisting entirely of carbon and hydrogen, such as methane (CH4).
    • Hydrocarbons are often used as fuels: the propane in a gas grill or the butane in a lighter.
    • The hydrocarbons discussed so far have been aliphatic hydrocarbons, which consist of linear chains of carbon atoms.
    • Another type of hydrocarbon, aromatic hydrocarbons, consists of closed rings of carbon atoms.
    • Some hydrocarbons have both aliphatic and aromatic portions; beta-carotene is an example of such a hydrocarbon.
  • 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.
  • 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.
  • Cycloalkanes

    • Cycloalkanes are saturated hydrocarbons that contain a ring in their carbon backbones.
    • Cycloalkanes are saturated hydrocarbons that contain a ring in their carbon backbones.
    • However, unlike linear hydrocarbons, which can achieve a more stable tetrahedral configuration around each carbon atom in the backbone, the bond angles in cycloalkanes are constrained, producing ring strain.
    • Hydrocarbons with two rings are called bicyclic, and well-known examples are norbornane and decalin.
  • Cycloalkanes

    • Hydrocarbons having more than one ring are common, and are referred to as bicyclic (two rings), tricyclic (three rings) and in general, polycyclic compounds.
    • In general, for a hydrocarbon composed of n carbon atoms associated with m rings the formula is: CnH(2n + 2 - 2m).
    • The structural relationship of rings in a polycyclic compound can vary.
  • 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.
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