Azulene
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| Azulene | |
|---|---|
| Chemical name | bicyclo[5.3.0]decapentaene |
| Chemical formula | C10H8 |
| Molecular mass | 128.17 g/mol |
| Melting point | 99 - 100 °C |
| Boiling point | 242 °C |
| Density | g/cm3 |
| CAS number | 275-51-4 |
| SMILES | C12=CC=CC=CC1=CC=C2 |
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| Disclaimer and references | |
Azulene is an organic compound whose molecules contain 10 carbons and 8 hydrogens and consist of a five-membered ring fused to a seven-membered ring. It is a monoterpene. It is an isomer of naphthalene but its physical properties are quite different. Naphthalene is a white crystalline solid whereas azulene, whose name is derived from the Spanish word azul, meaning "blue", is a dark blue crystalline solid used in many cosmetics. Azulene has a long history dating back to the 15th century as the azure-blue distillate obtained by steam distillation of Chamomile. The compound was discovered and named in 1863 by Septimus Piesse in azure-blue distillates from other sources such as yarrow and wormwood. Lavoslav Ružička solved the structure for this compound and the first organic synthesis followed in 1937 by Placidus Plattner.
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[edit] Derivatives
Vetivazulene or 4,8-dimethyl-2-isopropylazulene is obtained from vetiver oil. Guaiazulene or 1,4-dimethyl-7-isopropylazulene occurs naturally as a constituent of guaiac wood oil.
[edit] Structure
Azulene consists of a fused cyclopentadiene ring and a cycloheptatriene ring and is an isomer of naphthalene. Azulene is 10 pi electron system just like cyclodecapentaene and does have aromatic properties even though it is not a single ring system like benzene. The peripheral bonds have similar lengths and only the shared bond in the middle is a single bond. The stability gain from aromaticity is half of that of naphthalene. The molecule can be considered a fusion product of a 6 pi electron cyclopentadienide anion which is aromatic and the likewise aromatic 6 pi electron tropylium cation. The observed dipole moment of 1.0 Debye is consistent with this picture.
[edit] Organic synthesis
For many years not many synthetic routes existed to azulene and the compound was therefore expensive. A recent contribution takes cycloheptatriene as starting material [1].
In naphth[a]azulenes, a naphthalene ring is condensed with the 1,2-position of an azulene ring. In one such system [2] deformation from planarity is found similar to that of tetrahelicene.
[edit] External links
[edit] References
- ^ Approach to the Blues: A Highly Flexible Route to the Azulenes Sébastien Carret, Aurélien Blanc, Yoann Coquerel, Mikaël Berthod, Andrew E. Greene, Jean-Pierre Deprés Angewandte Chemie International Edition Volume 44, Issue 32 , Pages 5130 - 5133 2005 Abstract
- ^ Novel Synthesis of Benzalacetone Analogues of Naphth[a]azulenes by Intramolecular Tropylium Ion-Mediated Furan Ring-Opening Reaction and X-ray Investigation of a Naphth[1,2-a]azulene Derivative Kimiaki Yamamura, Shizuka Kawabata, Takatomo Kimura, Kazuo Eda, and Masao Hashimoto J. Org. Chem.; 2005; 70(22) pp 8902 - 8906; (Article) DOI: 10.1021/jo051409f Abstract
