Azulene is an organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 and an isomer

Valence isomer

In organic chemistry, two molecules are valence isomers when they are constitutional isomers that can interconvert through pericyclic reactions.-Benzene:...

 of naphthalene

Naphthalene

Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...

. Whereas naphthalene is colourless, azulene is dark blue. Its name is derived from the Spanish word azul

Azul

Azul means "blue" in Portuguese and Spanish and may refer to:* Azul..., a poetry collection by Rubén Darío* Azul Azul, a Bolivian pop-dance music group* Azul, Buenos Aires Province, a town in Argentina...

, meaning "blue". Two terpenoids, vetivazulene

Vetivazulene

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

 (4,8-dimethyl-2-isopropylazulene) and guaiazulene

Guaiazulene

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....

 (1,4-dimethyl-7-isopropylazulene), that feature the azulene skeleton are found in nature as constituents of pigments in mushrooms, guaiac wood oil

Oil of guaiac

Oil of guaiac is a fragrance used in soap. It comes from the palo santo tree .Oil of guaiac is produced through steam distillation of a mixture of wood and sawdust from palo santo. It is sometimes incorrectly called guaiac wood concrete. It is a yellow to greenish yellow semi-solid mass which...

, and some marine invertebrates.

Azulene has a long history, dating back to the 15th century as the azure-blue chromophore

Chromophore

A chromophore is the part of a molecule responsible for its color. The color arises when a molecule absorbs certain wavelengths of visible light and transmits or reflects others. The chromophore is a region in the molecule where the energy difference between two different molecular orbitals falls...

 obtained by steam distillation

Steam distillation

Steam distillation is a special type of distillation for temperature sensitive materials like natural aromatic compounds....

 of German chamomile.