Coronene

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Coronene
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Template:Longitem Template:Chembox Elements/molecular formula
Molar mass Template:Chem molar mass
Appearance Yellow powder[2]
Density 1.371 g/cm3[2]
Melting point Template:Chembox CalcTemperatures
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Solubility Very soluble: benzene, toluene, hexane,[4]
Chloroform (1 mmol·L−1)[5] and ethers, sparingly soluble in ethanol.
log P 7.38[6]
Band gap 1.7 eV[7]
Template:Longitem −243.3·10−6 cm3/mol
Template:Longitem Monoclinic
Template:Longitem P21/n
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a = 10.02 Å, b = 4.67 Å, c = 15.60 Å
α = 90°, β = 106.7°, γ = 90°
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Coronene (also known as superbenzene and cyclobenzene) is a polycyclic aromatic hydrocarbon (PAH) comprising seven peri-fused benzene rings.[8] Its chemical formula is Template:Chem/link. It is a yellow material that dissolves in common solvents including benzene, toluene, and dichloromethane. Its solutions emit blue light fluorescence under UV light. It has been used as a solvent probe, similar to pyrene.

The compound is of theoretical interest to organic chemists because of its aromaticity. It can be described by 20 resonance structures 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

File:Carpathite-258272.jpg
Carpathite

Coronene occurs naturally as the very rare mineral carpathite, characterized by flakes of pure coronene embedded in sedimentary rock. This mineral may be created from ancient hydrothermal vent activity.[9] In earlier times this mineral was also called karpatite or pendletonite.[10]

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.[11]

Coronene is produced in the petroleum-refining process of hydrocracking, 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.[12]

Structure

File:Coronene crystals luminescence.jpg
Crystals of β and γ coronene under daylight (left) and UV light (right)[12]

Coronene is a planar circulene. 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)[12] or by phase transition from γ decreasing the temperature below 158 K.[13] The structure containing two C-H groups on one benzene ring, so-called DUO, was analyzed by infrared spectroscopy.[14]

Other uses

File:Coronene MOF.jpg
Structure and electron micrograph of a coronene-based metal–organic framework

Coronene has been used in the synthesis of graphene. 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.[15]


See also

References

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  1. ↑ Script error: No such module "citation/CS1".
  2. ↑ a b Haynes, p. 3.128
  3. ↑ Haynes, p. 5.145
  4. ↑ Bertarelli, Chiara. Molecules for organic electronics: intermolecular interactions vs properties. Dipartimento di Chimica, Politecnico di Milano
  5. ↑ Script error: No such module "Citation/CS1".
  6. ↑ Chemspider, https://legacy.chemspider.com/Chemical-Structure.8761.html
  7. ↑ Haynes, p. 12.95
  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ Karpatite. luminousminerals.com
  10. ↑ Carpathite. mindat.org
  11. ↑ Script error: No such module "Citation/CS1".
  12. ↑ a b c Script error: No such module "Citation/CS1".
  13. ↑ Script error: No such module "Citation/CS1".
  14. ↑ Script error: No such module "Citation/CS1".
  15. ↑ Script error: No such module "Citation/CS1".

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Cited sources

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