- Sep 30, 2017 -
Azulene is an organic compound and isomer of naphthalene. Naphthalene is colorless, azulene is dark blue. Two terpenoids, characterized in that the cucumber skeleton of the grapefruit is found in nature as a component of mushrooms, guaiac and some marine invertebrates.
Azulene has a long history, dating back to the 15th century, by the German chamomile steam distillation of blue blue chromophores. The chromophore was found in yarrow and artemisin and was named after Septimus Piesse in 1863. Its structure was first reported by LavoslavRužička, followed by organic synthesis by Placidus Plattner in 1937.
1 structure and bonding
2 organic synthesis
3 Organometallic complexes
4 related compounds
6 External links
Structure and combination
The blue color of the mushroom cyanobacteria is due to the azulene derivative (7-isopropenyl-4-methyl azulen-1-yl) methyl stearate. 
Azulene is generally believed to be produced by the fusion of cyclopentadiene and cycloheptatriole rings. Like naphthalene and cyclopentadecene, it is a 10 pi electronic system. It exhibits aromatic properties: (i) peripheral keys have similar lengths, (ii) it undergoes Friedel-Crafts-like substitutions. The aromatic stability gain is estimated to be half of naphthalene.
Its dipole moment is 1.08D,  compared with naphthalene, its dipole moment is zero. This polarity can be explained by the combination of azulene as a 6π electron cyclopentadienyl anion and a 6π electron propyl ammonium cation: an electron from the seven membered ring is transferred to a five membered ring to give each ring aromatic stable By the rule of Hückel. Reactivity studies confirm that the seven-membered ring is electrophilic and the five-membered ring is nucleophilic.
The dipole of the ground state is reflected in its darkness, which is unusual for small unsaturated aromatic compounds. Another significant feature of azulene is that it violates the law of sand by reflecting the fluorescence (S2 → S0) in the highly excited state. 
Due to its unusual structure, the synthesis route to azulene has long been of interest. In 1939, the first method was reported by St.Pfau and Plattner , starting with indane and ethyl diazoacetate.
An effective boiler route requires the copolymerization of cyclopentadiene with the unsaturated C5-composition.  A long way to know the alternative method of cycloheptatriene, an illustrative method as shown below