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An '''aromatic ring''' is a [[hydrocarbon]], such as [[benzene]], that has a low [[hydrogen]] to [[carbon]] ratio, and has low chemical reactivity due to aromatic resonance. In the case of benzene (formula C<sub>6</sub>H<sub>6</sub>), the carbon atoms form a hexagonal ring, with each carbon atom bonded in series at each point of the hexagon. Because of orbital hybridization, each carbon atom can bond to only one hydrogen. Although the traditional illustration of an aromatic ring appears to contain double bonds, in reality the extra pi electrons are equally distributed around the ring because of resonance. This results in an exceptionally stable molecule which does not undergo markovnikovian addition reactions. There are other shapes as well, including cyclooctatetraene, an octagonal aromatic ring, where the same ratio applies.
An '''aromatic ring''' is a [[hydrocarbon]], such as [[benzene]], that has a low [[hydrogen]] to [[carbon]] ratio, and has low chemical reactivity due to aromatic resonance. In the case of benzene (formula C<sub>6</sub>H<sub>6</sub>), the carbon atoms form a hexagonal ring, with each carbon atom bonded in series at each point of the hexagon. Because of orbital hybridization, each carbon atom can bond to only one hydrogen. Although the traditional illustration of an aromatic ring appears to contain double bonds, in reality the extra pi electrons are equally distributed around the ring because of resonance. This results in an exceptionally stable molecule which does not undergo markovnikovian addition reactions.
There are variations to the benzene molecule. One such variation is [[toluene]] (formula C<sub>7</sub>H<sub>8</sub>, also called methylbenzene) where a [[methyl]] group replaces a hydrogen atom. Other variations can have non-carbon substituents in the ring whose free electron pairs contribute to the de-localized aromatic field.
There are other shapes as well, but in order to be aromatic the ring must satisfy Huckel's rule by having a number of free electrons which satisfies the equation 4N+2. Cyclooctotetraene is an example of a molecule which does not follow this rule. Although it is a ring composed of alternating double bonds, it's chemical reactivity is that of a non-aromatic alkene.
Aromatic rings can also form in groups or chains, where each ring is "joined at the hip." These are called ''polycyclic benzenoid aromatic hydrocarbons''. One such case is naphthalene (formula C<sub>10</sub>H<sub>8</sub>), where two benzene rings share one carbon bond.
There are variations to the benzene molecule. One such variation is [[toluene]] (formula C<sub>7</sub>H<sub>8</sub>, also called methylbenzene) where a [[methyl]] group replaces a hydrogen atom. Other variations can have non-carbon substituents in the ring whose free electron pairs contribute to the de-localized aromatic field and help it satisfy Huckel's rule.
Aromatic rings can also form in groups or chains, where each ring is "joined at the hip." These are called ''polycyclic benzenoid aromatic hydrocarbons''. One such case is naphthalene (formula C<sub>10</sub>H<sub>8</sub>), where two benzene rings share one carbon bond. These compounds must also follow Huckel's rule in order to be aromatic.
Aromatic rings were called ''aromatic'' in the early days of their discovery because they are [[fragrant]], as they were obtained from resins or oils.
Aromatic rings were called ''aromatic'' in the early days of their discovery because they are [[fragrant]], as they were obtained from resins or oils.
[[Category:Organic Chemistry]]
[[Category:Organic Chemistry]]