Annulene
Annulenes are
The discovery that [18]annulene possesses a number of key properties associated with other aromatic molecules was an important development in the understanding of aromaticity as a chemical concept.
In the related annulynes, one double bond is replaced by a triple bond.
Aromaticity
n | aromaticity |
---|---|
4 | antiaromatic |
6 | aromatic |
8 | nonaromatic |
10 | nonaromatic |
12 | weakly antiaromatic |
14 | weakly aromatic |
16 | nonaromatic[4] |
18 | aromatic |
Annulenes may be
When the annulene is large enough, [18]annulene for example, there is enough room internally to accommodate hydrogen atoms without significant distortion of bond angles. [18]Annulene possesses several properties that qualify it as aromatic.[5] However, none of the larger annulenes are as stable as benzene, as their reactivity more closely resembles a conjugated polyene than an aromatic hydrocarbon.
In general, charged annulene species of the form [C4n+2+qH4n+2+q]q (n = 0, 1, 2, ..., q = 0, ±1, ±2, 4n + 2 + q ≥ 3) are aromatic, provided a planar conformation can be achieved. For instance, C5H5–, C3H3+, and C8H82– are all known aromatic species.
Gallery
-
Cyclobutadiene ([4]annulene)
-
Benzene ([6]annulene)
-
Cyclooctatetraene ([8]annulene)
-
Cyclododecahexaene ([12]annulene)
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Cyclotetradecaheptaene ([14]annulene)
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Cyclooctadecanonaene ([18]annulene)
-
Cyclodocosahendecaene ([22]-annulene)
See also
References
External links
- NIST Chemistry WebBook - [18]annulene
- Structure of [14] and [18]annulene