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Chemical compound From Wikipedia, the free encyclopedia
Kekulene is a polycyclic aromatic hydrocarbon which consists of 12 fused benzene rings arranged in a circle. It is therefore classified as a [12]-circulene with the chemical formula C48H24. It was first synthesized in 1978,[2] and was named in honor of August Kekulé, the discoverer of the structure of the benzene molecule.
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Names | |||
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Preferred IUPAC name
15,23:16,22-Di(metheno)naphtho[2,3-a]tetrapheno[3,2-o]pentaphene | |||
Other names
[12]–Coronaphen, [12]Circulene | |||
Identifiers | |||
3D model (JSmol) |
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ChEBI | |||
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PubChem CID |
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CompTox Dashboard (EPA) |
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Properties | |||
C48H24 | |||
Molar mass | 600.720 g·mol−1 | ||
Density | 1.46 g/cm3 (calc.)[1] | ||
Structure[1] | |||
monoclinic, C2/c | |||
a = 2795.1(4) pm, b = 457.9(1) pm, c = 2268.0(2) pm α = 90°, β = 109.64(1)°, γ = 90° | |||
Formula units (Z) |
4 | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The nature of the π bonding within the molecule was long debated, as several distinctly different arrangements were possible. The two most significant proposals are the "Clar" configuration, consisting of six benzene-like (aromatic 6 π-electron) rings connected by bridging bonds and vinyl groups in non-aromatic rings, and the "Kekulé" configuration, consisting of two concentric aromatic rings (18 π-electron inner, 30 π-electron outer) linked by radial single bonds.[3][4][5][6][7][8][9]
The synthesis of the compound, first reported in 1978,[5] allowed experimental determination of the electronic structure. In the late 1970s, 1H-NMR provided evidence of benzene rings[5] and X-ray analysis determined that the structure had had alternating aromatic and non-aromatic rings,[3] both consistent with the Clar configuration. In 2019, the configuration was determined to be one consisting of benzene-like rings alternating with non-aromatic linkages, by using single molecule atomic force microscopy to measure the carbon–carbon bond-lengths and bond orders.[10] This configuration is in keeping with Clar's rule, as it has the largest number of disjoint aromatic π sextets.
Though the whole structure is essentially planar, it only has three-fold symmetry rather than six-fold. The carbon–hydrogen bonds in the center of the ring have a slight alternating tilt out of the plane to avoid steric hindrance among the hydrogen atoms.[10]
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