Azulenes

Azulene is an aromatic organic compound and an isomer of naphthalene. Naphthalene is colourless, whereas azulene is dark blue. The compound is named after its colour, as "azul" is Spanish for blue. Two terpenoids, vetivazulene (4,8-dimethyl-2-isopropylazulene) and guaiazulene (1,4-dimethyl-7-isopropylazulene), that feature the azulene skeleton are found in nature as constituents of pigments in mushrooms, guaiac wood oil, and some marine invertebrates.

Guaiazulene, also azulon or 1,4-dimethyl-7-isopropylazulene, is a dark blue crystalline hydrocarbon. A derivative of azulene, guaiazulene is a bicyclic sesquiterpene that is a constituent of some essential oils, mainly oil of guaiac and chamomile oil, which also serve as its commercial sources. Various soft corals also contain guaiazulene as a principal pigment. Its low melting point makes guaiazulene difficult to handle, in contrast to the crystalline nature of the parent azulene. The electronic structure (and colors) of guaiazulene and azulene are very similar.

Chamazulene is an aromatic chemical compound with the molecular formula C14H16 found in a variety of plants including in chamomile (Matricaria chamomilla), wormwood (Artemisia absinthium), and yarrow (Achillea millefolium). It is a blue-violet derivative of azulene formed from sesquiterpene matricin after the loss of acetate, water and carbon dioxide during the steam distillation of chamomile blossoms. Oral ingestion of matricin results in chamazulene being found in blood plasma and artificial gastric fluid is able to convert matricin to chamazulene.

Vetivazulene is an azulene derivate obtained from vetiver oil. It is a bicyclic sesquiterpene and an isomer of guaiazulene.

Purpurogallin is an aglycone natural product. It is an orange-red solid that is soluble in polar organic solvents but not in water. Its glycoside (ether-linked to sugar), called dryophantin, is found in nutgalls and oak barks. Purpurogallin can be prepared by oxidation of pyrogallol with sodium periodate.

Carotol was first isolated by scientists Asahina and Tsukamoto in 1925. It is one of the primary components found in carrot seed oil comprising approximately 40% of this essential oil. This sesquiterpene alcohol is thought to be formed in carrot seeds (Daucus carota L., Umbelliferae) during the vegetation period. Additionally, studies have shown that carotol may be involved in allelopathic interactions expressing activity as an antifungal, herbicidal and insecticidal agent.