Coronene

Coronene is a polycyclic aromatic hydrocarbon consisting of seven peri-fused benzene rings ^[1]. It is a yellow material, which dissolves in solvents such as benzene, toluene, and dichloromethane. Its solutions give blue light fluorescence under UV light. Its emission spectrum is not symmetrical with its excitation spectrum and varies in the number of bands and their relative intensities with solvent. It has been used as a solvent probe, similarly to pyrene.

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It occurs naturally as the mineral carpathite, which is characterized by flakes of pure coronene embedded in sedimentary rock. This mineral may result from ancient hydrothermal vent activity. ^{[2] [3]}.

Coronene is produced in the petroleum refining process of hydrocracking, where it can dimerize to a fifteen ring PAH, trivially named "dicoronylene" (formally named benzo[10,11]phenanthro[2',3',4',5',6':4,5,6,7]chryseno[1,2,3-bc]coronene or benzo[1,2,3-bc:4,5,6-b'c']dicoronene). Coronene has been seen on the surface of Titan^{[citation needed]} (Saturn's moon). It can cause DNA damage in mammals^{[citation needed]}.

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 latter case the most stable structure for coronene has only the three isolated outer sextets as fully aromatic although superaromaticity would still be possible when these sextets are able to migrate into the next ring.

According to in silico calculations on the following hypothetical isodesmic reactions coronene has a somewhat higher resonance energy per pi electron (REPE) than benzene ^[4]:

coronene + 24 * ethylene -> 18 * butadiene REPE 4.2 kcal/mol (17.6 kJ/mol)

benzene + 3 * ethylene -> 3 * butadiene REPE 3.6 kcal/mol (15 kJ/mol)

On the other hand the perimeter C–C bond length alternations are larger than in benzene.

Hexa-benzopericoronenes

Hexa-benzopericoronenes are members of the coronene family and investigated in supramolecular electronics. They are known to self-assemble into a columnar phase. One derivative in particular forms nanotubes with interesting electrical properties ^[5]. The columnar phase in this compound further organises itself into sheets which ultimately roll up like a carpet to form multi-walled nanotubes with an outer diameter of 20 nanometer and a wall thickness of 3 nanometer. In this geometry the stacks of coronene disks are aligned with the length of the tube. The nanotubes have sufficient length to fit between two platinum nanogap electrodes produced by scanning probe nanofabrication and are 180 nanometer apart. The nanotubes as such are insulating but after one-electron oxidation with nitrosonium tetrafluoroborate (NOBF₄) they conduct electricity.

Organic synthesis of a hexa-benzopericoronene starts with an Aldol condensation reaction of an acetone derivative with a benzil derivative to substituted cyclopentadienone. This compound is reacted with an alkyne in a Diels-Alder reaction and subsequent expulsion of carbon monoxide to the hexaphenylbenzene which is oxidized by Iron(III) chloride in nitromethane

See also

• A related compound lacking the central core: cyclooctadecanonaene
• Coronene's dimer: Dicoronylene

References