Zethrene () is a

polycyclic aromatic hydrocarbon A Polycyclic aromatic hydrocarbon (PAH) is any member of a class of organic compounds that is composed of multiple fused aromatic rings. Most are produced by the incomplete combustion of organic matter— by engine exhaust fumes, tobacco, incine ...

consisting of two

phenalene 1''H''-Phenalene, often called simply phenalene is a polycyclic aromatic hydrocarbon (PAH). Like many PAHs, it is an atmospheric pollutant formed during the combustion of fossil fuels. It is the parent compound for the phosphorus-containing phos ...

units fused together. According to

Clar's rule In organic and physical organic chemistry, Clar's rule is an empirical rule that relates the chemical stability of a molecule to its aromaticity. It was introduced in 1972 by the Austrian organic chemist Erich Clar in his book ''The Aromatic Sext ...

, the two exterior

naphthalene Naphthalene is an organic compound with formula . It is the simplest polycyclic aromatic hydrocarbon, and is a white Crystal, crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 Parts-per notation ...

units are truly aromatic and the two central

double bonds In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist betwee ...

are not aromatic at all. For this reason the compound is of some interest to academic research. Zethrene has a deep-red color and it is light sensitive - complete decomposition under a sunlight lamp occurs within 12 hours. The

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

is 262 °C.

Synthesis

The compound was originally synthesized by

Erich Clar Erich Clar (23 August 1902 – 27 March 1987) was a German organic chemistry, organic chemist, born in Hřensko (a village directly at the border of Germany and the Czech Republic; Czech: Hřensko, German: Herrnskretschen), who studied polycyclic a ...

in 1955 from

acenaphthene Acenaphthene is a polycyclic aromatic hydrocarbon (PAH) consisting of naphthalene with an ethylene bridge connecting positions 1 and 8. It is a colourless solid. Coal tar consists of about 0.3% of this compound. Production and reactions Acenaph ...

in one method and from

chrysene Chrysene is a polycyclic aromatic hydrocarbon (PAH) with the molecular formula that consists of four fused benzene rings. It is a natural constituent of coal tar, from which it was first isolated and characterized. It is also found in creosote ...

in another. Mitchell and Sondheimer prepared the compound from a benzannulated 0nnulene. A sulfur extrusion method was reported by Kemp, Storie, and Tulloch. Wu et al. reported the synthesis of the compound in a

coupling reaction In organic chemistry, a coupling reaction is a type of reaction in which two reactant molecules are bonded together. Such reactions often require the aid of a metal catalyst. In one important reaction type, a main group organometallic compound o ...

/ dimerization with in-situ desilylation. A Heck variation was reported in 2013. Derivatives are also known.

Structure

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

indicates that zethrene is a planar molecule. The bond lengths in the central part of the molecule are consistent with distinct single and double bonds rather than aromatic components.

References

{{PAHs Polycyclic aromatic hydrocarbons Hexacyclic compounds