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( Aromatic hydrocarbon)
An aromatic hydrocarbon (abbreviated as AH) or arene [1] is a hydrocarbon, of which the molecular structure incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent. This sweet scent actually came from impurities in the compounds (which are not actually aromatic in the sense initially described). The configuration of six carbon atoms in aromatic compounds is known as a benzene ring, after the simplest possible such hydrocarbon, benzene. Aromatic hydrocarbons can be monocyclic or polycyclic. Some non-benzene-based compounds called heteroarenes, which follow Hückel's rule, are also aromatic compounds. In these compounds, at least one carbon atom is replaced by one of the heteroatoms oxygen, nitrogen, or sulfur. Examples of non-benzene compounds with aromatic properties are furan, a heterocyclic compound with a five-membered ring that includes an oxygen atom, and pyridine, a heterocyclic compound with a six-membered ring containing one nitrogen atom.[2] Many chemists draw a circle around the inside of the ring to show six electrons floating around in delocalized molecular orbitals the size of the ring itself. This also accurately represents the equivalent nature of the six bonds all of bond order ~1.5. This equivalency is well explained by resonance forms. The electrons float above and below the ring, and the electromagnetic fields they generate keep the ring flat. General properties Many laboratory methods exist for the organic synthesis of arenes from non-arene precursors
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