stabilize charges. This is seen in, for example, phenol (C6H5–OH), which is acidic at the hydroxyl (OH), since a charge on this oxygen (alkoxide –O−) is partially delocalized into the benzene ring. Other monocyclic aromatic hydrocarbon Other monocyclic aromatic hydrocarbon include Cyclotetradecaheptaene or Cyclooctadecanonaene. Polycyclic aromatic hydrocarbons Polynuclear aromatic hydrocarbons (PAHs) are aromatic hydrocarbons that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH. PAHs occur in oil, coal, and tar deposits, and are produced as byproducts of fuel burning (whether fossil fuel or biomass). As pollutants, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic. PAHs are also found in cooked foods. Studies have shown that high levels of PAHs are found, for example, in meat cooked at high temperatures such as grilling or barbecuing, and in smoked fish. They are also found in the interstellar medium, in comets, and in meteorites and are a candidate molecule to act as a basis for the earliest forms of life. In graphene the PAH motif is extended to large 2D sheets. See also Aromatic substituents: Aryl, Aryloxy and Arenediyl Asphaltene Hydrodealkylation Simple aromatic rings Rhodium-platinum oxide, a catalyst used to hydrogenate aromatic compounds. References External links