Introduction of Aromatic Hydrocarbons
Aromatic hydrocarbons are the hydrocarbons that have delocalized pi electrons and the sigma bonds between the carbon atoms in the form of circles. These are called aromatic due to their characteristic pleasant or sweet odor. In the aromatic compounds, the configuration of six carbon atom is known to make the benzene ring. Aromatic hydrocarbons can be either monocyclic or polycyclic. These are the ring compounds in which all the ring atoms do participate in the form of latex bonds and result in the unusual stability. As compare to alkanes, these compounds are less reactive, so, they are of greater importance as industrial solvents for the non-polar compounds. Usually, aromatic compounds are produced from coal tar and petroleum. They are represented in the form of resonance structures, that contains the single and double bonds. However, other than the expected strength for the conjugated structure, the bonding is much stronger.
Aromatic compounds are the class of hydrocarbons and they possess greater stability than their conjugated unsaturated system suggestions. Benzene is the simplest example of the class of hydrocarbons, which was isolated in 1825 by Michael Faraday from the illuminating gas. He found this compound in the liquid residue which was condensed from the gaseous phase when the whale oil was burnt in the street lamps of London. The compounds of aromatic hydrocarbons are cyclic structures and the rings are planar unlike the table or boat structure of the typical cycloalkanes. Generally, these compounds are non-polar and are immiscible in the water. Often, they are unreactive and the ratio of carbon to hydrogen in these compounds is high so they are characterized by a flame that is sooty yellow in color. These compounds are produced from the variety of sources and generally, the polyaromatic hydrocarbons are carcinogens and are component of the atmospheric pollution.
Nowadays there are many naturally occurring and synthetic aromatic compounds that are benzene, benzaldehyde, toluene, oestrone, morphine, and diazepam (Valium), etc. There are many aromatic compounds which we commonly come in touch to, such as saccharine that is the synthetic sweetener, benzopyrene that is the carcinogenic compound and is formed during the boiling of the meat, 2,4,5- trichloro phenoxy acetic acid, the anthraquinone dye that is 1,4-diaminoanthraquinone and is used to dye hair purple. Defoliant is the derivative of acetic acid and it was used during the war in Vietnam. For its synthesis, 2,3,7,8-tetrachlorodibenzo[b,e]-p-dioxin appears that is the Seveso poison. The dioxin is also produced as a by-product when the chlorine-containing aromatic compounds are burnt improperly in the incineration plant.
Currently, in the chemical aspect, the term of aromatic is no longer correlated with the smell of the compounds. Now, this term is applied to the family of the compounds whose compounds are structurally related to those which contain an aromatic system. Considerably, the chemical behavior of the aromatic compounds is different from that of the aliphatic compounds. The aromatic compound, benzene is toxic, even in the small concentrations, therefore, great precautions should be taken, while working with this compound.
