Azulene

Azulene is an organic compound with the formula C10H8. It is a nonbenzenoid bicyclic aromatic hydrocarbon that is an isomer of naphthalene. Unlike naphthalene’s two fused benzene rings, azulene comprises a five-membered ring fused to a seven-membered ring, giving a distinctive geometry and a deep blue color in its pure form.

The molecule contains 10 pi electrons and is considered aromatic, though its nonstandard ring system gives it unique electronic properties. Azulene exhibits a noticeable dipole moment and a characteristic charge distribution, which contribute to its reactivity compared with other hydrocarbons of similar formula. The compound is relatively stable under normal conditions but participates in typical aromatic reactions, including electrophilic substitutions at activated positions.

Azulene and its derivatives occur in nature primarily as components of essential oils. In chamomile oil, the blue coloration arises from chamazulene, a bicyclic azulene derivative formed during the steam distillation of matricin. This natural occurrence helps explain the characteristic blue hue associated with chamomile extracts.

Applications of azulene derivatives include the production of blue dyes and pigments used in inks and coatings. The azulene framework also serves as a synthetic scaffold in organic chemistry and materials science, where derivatives are explored for potential use in organic electronics and as intermediates in the preparation of more complex aromatic compounds.

Safety and handling align with standard organic hydrocarbons; derivatives can have varying toxicological profiles, so appropriate laboratory precautions are advised.