Cannabaceae

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Kekulene
Names
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)
ChEBI
ChemSpider
  • InChI=1S/C48H24/c1-2-26-14-28-5-6-30-16-32-9-10-34-18-36-12-11-35-17-33-8-7-31-15-29-4-3-27-13-25(1)37-19-39(27)41(29)21-43(31)45(33)23-47(35)48(36)24-46(34)44(32)22-42(30)40(28)20-38(26)37/h1-24H ☒N
    Key: TYPKKLUFDMGLAC-UHFFFAOYSA-N ☒N
  • InChI=1/C48H24/c1-2-26-14-28-5-6-30-16-32-9-10-34-18-36-12-11-35-17-33-8-7-31-15-29-4-3-27-13-25(1)37-19-39(27)41(29)21-43(31)45(33)23-47(35)48(36)24-46(34)44(32)22-42(30)40(28)20-38(26)37/h1-24H
    Key: TYPKKLUFDMGLAC-UHFFFAOYAP
  • C1=CC2=CC3=C4C=C2C5=CC6=C(C=CC7=CC8=C(C=C76)C9=CC2=C(C=CC6=C2C=C2C(=C6)C=CC6=C2C=C4C(=C6)C=C3)C=C9C=C8)C=C51
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°
4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

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.

Geometry and electronic structure[edit]

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]

  • Proposed electronic configurations
  • "Kekulé" configuration: Two concentric aromatic rings
    "Kekulé" configuration: Two concentric aromatic rings
  • "Clar" configuration: Benzene rings alternating with non-aromatic linkers
    "Clar" configuration: Benzene rings alternating with non-aromatic linkers

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]

References[edit]

  1. ^ a b Staab, Heinz A.; Diederich, François; Krieger, Claus; Schweitzer, Dieter (1983). "Cycloarenes, a New Class of Aromatic Compounds, II. Molecular Structure and Spectroscopic Properties of Kekulene". Chemische Berichte. 116 (10): 3504–3512. doi:10.1002/cber.19831161022.
  2. ^ Staab, Heinz A.; Diederich, François (October 1983). "Cycloarenes, a New Class of Aromatic Compounds, I. Synthesis of Kekulene". Chemische Berichte. 116 (10): 3487–3503. doi:10.1002/cber.19831161021.
  3. ^ a b Krieger, Claus; Diederich, Francois; Schweitzer, Dieter; Staab, Heinz A. (September 1979). "Molecular Structure and Spectroscopic Properties of Kekulene". Angewandte Chemie International Edition in English. 18 (9): 699–701. doi:10.1002/anie.197906991.
  4. ^ Aihara, Junichi (January 1992). "Is superaromaticity a fact or an artifact? The kekulene problem". Journal of the American Chemical Society. 114 (3): 865–868. doi:10.1021/ja00029a009.
  5. ^ a b c Diederich, François; Staab, Heinz A. (May 1978). "Benzenoidversus Annulenoid Aromaticity: Synthesis and Properties of Kekulene". Angewandte Chemie International Edition in English. 17 (5): 372–374. doi:10.1002/anie.197803721.
  6. ^ Jiao, Haijun; Schleyer, Paul von Ragué (1 November 1996). "Is Kekulene Really Superaromatic?". Angewandte Chemie International Edition in English. 35 (20): 2383–2386. doi:10.1002/anie.199623831.
  7. ^ Schweitzer, D.; Hausser, K.H.; Vogler, H.; Diederich, F.; Staab, H.A. (11 August 2006). "Electronic properties of kekulene". Molecular Physics. 46 (5): 1141–1153. doi:10.1080/00268978200101861.
  8. ^ Staab, Heinz A.; Diederich, FrançOis; Krieger, Claus; Schweitzer, Dieter (October 1983). "Cycloarenes, a New Class of Aromatic Compounds, II. Molecular Structure and Spectroscopic Properties of Kekulene". Chemische Berichte. 116 (10): 3504–3512. doi:10.1002/cber.19831161022.
  9. ^ Zhou, Zhongxiang (February 1995). "Are kekulene, coronene, and corannulene tetraanion superaromatic? Theoretical examination using hardness indices". Journal of Physical Organic Chemistry. 8 (2): 103–107. doi:10.1002/poc.610080209.
  10. ^ a b Pozo, Iago; Majzik, Zsolt; Pavliček, Niko; Melle-Franco, Manuel; Guitián, Enrique; Peña, Diego; Gross, Leo; Pérez, Dolores (17 September 2019). "Revisiting Kekulene: Synthesis and Single-Molecule Imaging". Journal of the American Chemical Society. 141 (39): 15488–15493. doi:10.1021/jacs.9b07926. PMC 6786662. PMID 31525873.
source: https://en.wikipedia.org/wiki/Kekulene

One thought on “Cannabaceae”

  1. Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
    View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction

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