aromatic compound

aromatic compound

aromatic compound, any of a large class of compounds that includes benzene and compounds that resemble benzene in certain of their chemical properties. Originally applied to a small class of pleasant-smelling chemicals derived from vegetables, it now encompasses a wide diversity of compounds with no connection to the sense of smell. Common aromatic compounds other than benzene include toluene, naphthalene, and anthracene (all of which are present in coal tar). Each of these compounds contains at least one ring that consists of six carbon atoms, each joined to at least two other carbon atoms, and each joined to adjacent carbon atoms by one single and one double bond. The resulting hexagonal structure is characteristic of many aromatic compounds. The general rule is that aromatic molecules have 4n + 2 delocalized electrons (where n is an integral number). Thus the number of delocalized electrons in benzene (6), naphthalene (10), and anthracene (14) agree with their aromatic character. On the other hand, the eight-membered cyclic compound with four alternating double bonds (cyclooctatetraene) is not aromatic and shows reactivity similar to alkenes. For this reason, the bonds in the aromatic ring are less reactive than ordinary double bonds; aromatic compounds tend to undergo ionic substitution (e.g., replacement of a hydrogen bonded to the ring with some other group) rather than addition (which would involve breaking one of the resonant bonds in the ring). Presence of the six-membered benzene ring is not essential for aromatic compounds; for example, furan, a heterocyclic compound that has a five-membered ring that includes an oxygen atom, has aromatic properties, as does pyridine, a heterocyclic compound whose six-membered ring includes a nitrogen atom.
In organic chemistry, compounds composed of carbon and hydrogen are divided into two classes: aromatic compounds, which contain benzene rings or similar rings of atoms, and aliphatic compounds (G. aleiphar, fat, oil), which do not contain aromatic rings.

In aliphatic compounds, carbon atoms can be joined together in straight chains, branched chains, or non-aromatic rings (in which case they are called alicyclic). They can be joined by single bonds (alkanes), double bonds (alkenes), or triple bonds (alkynes). Besides hydrogen, other elements can be bound to the carbon chain, the most common being oxygen, nitrogen, sulfur, and chlorine.

The simplest aliphatic compound is methane (CH4). Aliphatics include alkanes such as fatty acids and paraffin hydrocarbons, alkenes (such as ethylene) and alkynes (such as acetylene).

Most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in Bunsen burners, and acetylene in welding.


See also


Search another word or see aromatic compoundon Dictionary | Thesaurus |Spanish
Copyright © 2015, LLC. All rights reserved.
  • Please Login or Sign Up to use the Recent Searches feature