Coronene (also known as superbenzene and cyclobenzene) 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 ...

(PAH) comprising seven peri-fused

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

rings. Its chemical formula is . It is a yellow material that dissolves in common solvents including

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

, and

dichloromethane Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with ...

. Its solutions emit blue light

fluorescence Fluorescence is one of two kinds of photoluminescence, the emission of light by a substance that has absorbed light or other electromagnetic radiation. When exposed to ultraviolet radiation, many substances will glow (fluoresce) with colore ...

under

UV light Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of t ...

. It has been used as a solvent probe, similar to

pyrene Pyrene is a polycyclic aromatic hydrocarbon (PAH) consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is . This yellow-green solid is the smallest peri-fused PAH (one where the rings are fused thro ...

. The compound is of theoretical interest to organic chemists because of its

aromaticity In organic chemistry, aromaticity is a chemical property describing the way in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibits a stabilization stronger than would be expected from conjugation alone. The e ...

. It can be described by 20

resonance structures In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or ''forms'', also variously known as ''resonance structures'' or '' ...

or by a set of three mobile Clar sextets. In the Clar sextet case, most stable structure for coronene has only three isolated outer sextets as fully aromatic although superaromaticity would still be possible when these sextets are able to migrate into next ring.

Occurrence and synthesis

Coronene occurs naturally as the very rare

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

carpathite, characterized by flakes of pure coronene embedded in sedimentary rock. This mineral may be created from ancient hydrothermal vent activity. In earlier times this mineral was also called karpatite or pendletonite. The presence of coronene putatively formed from contact of magma with fossil fuel deposits has been used to argue that Permian-Triassic “ Great Dying” event was caused by a greenhouse gas warming episode triggered by large-scale Siberian vulcanism. Coronene is produced in the petroleum-refining process of

hydrocracking In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking ...

, where it can dimerize to a fifteen ring PAH, trivially named " dicoronylene" . Centimeter-long crystals can be grown from a supersaturated solution of molecules in toluene (ca. 2.5 mg/ml), which is slowly cooled (ca. 0.04 K/min) from 328 K to 298 K over a period of 12 hours.

Structure

Coronene is a planar

circulene A circulene is a macrocyclic arene in which a central polygon is surrounded and fused by benzenoids. Nomenclature within this class of molecules is based on the number of benzene rings surrounding the core, which is equivalent to the size of the ...

. It forms needle-like crystals with a monoclinic, herringbone-like structure. The most common polymorph is γ, but β form can also be produced in an applied magnetic field (ca. 1 Tesla) or by phase transition from γ decreasing the temperature below 158 K. The structure containing two C-H groups on one benzene ring, so-called DUO, was analyzed by infrared spectroscopy.

Other uses

Coronene has been used in the synthesis of

graphene Graphene () is a carbon allotrope consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice, honeycomb planar nanostructure. The name "graphene" is derived from "graphite" and the suffix -ene, indicating ...

. For example, coronene molecules evaporated onto a copper surface at 1000 degrees Celsius will form a graphene lattice which can then be transferred onto another substrate.

References

Cited sources

* {{PAHs Polycyclic aromatic hydrocarbons

Occurrence and synthesis

Structure

Other uses

See also

References

Cited sources