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

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.