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coronene

n. (context organic compound English) A polycyclic aromatic hydrocarbon consisting of six benzene rings fused together into a ring; any derivative of this compound.

Wikipedia
Coronene

Coronene (also known as superbenzene) is a polycyclic aromatic hydrocarbon (PAH) comprising six peri-fused benzene rings. Its chemical formula is . It is a yellow material that dissolves in such solvents as benzene, toluene, and dichloromethane. Its solutions emit 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 depending on the solvent. It has been used as a solvent probe, similar to pyrene.

It occurs naturally as the very rare mineral carpathite, which is 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.

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).

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, 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:

coronene + 24 * ethylene ā†’ 18 * butadiene REPE 4.2 kcal/ mol (17.6 kJ/mol) benzene + 3 * ethylene ā†’ 3 * butadiene REPE 3.6 kcal/mol (15 kJ/mol)

On the other hand, the perimeter Cā€“C bond length alternations are larger than in benzene.