Corannulene
Corannulene is a polycyclic aromatic hydrocarbon with chemical formula C20H10 [1]. The molecule consists of a cyclopentane ring fused with 5 benzene rings. It is of scientific interest because it is a geodesic polyarene and can be considered a fragment of buckminsterfullerene. Due to this connection and also its bowl shape, corannulene is also known as a buckybowl. Corannulene exhibits a bowl-to-bowl inversion with an inversion barrier of 10.2 Kcal/mole at -64 °C.
Several synthetic routes exist to corannulene. Flash vacuum pyrolysis techniques generally have low chemical yields but one organic synthesis exists based on solution chemistry [2] consisting of a nucleophilic displacement - elimination reaction of an octabromide with potassium hydroxide (fig. 1).
The bromine substituents are removed with an excess of n-butyllithium.
The observed aromaticity for this compound is explained with a so-called annulene-within-anannulene model. According to this model corannulene is made up of an aromatic 6 electron cyclopentadienyl anion surrounded by an aromatic 14 electron annulenyl cation. Corannulenes react with alkali metals in a series of one-electron reductions. The corannulene dianion is antiaromatic and tetraanion is again aromatic. With lithium as reducing agent two tetraanions form a supramolecular dimer with two bowls stacked into each other (convex-convex) and with 4 lithium ions in between and 2 pairs above and below the stack.
In one cyclopenta[bc]corannulene a concave - concave aggregate is observed by NMR spectroscopy with 2 C-Li-C bonds connecting the tetraanions [3].
![Cyclopenta[bc]corannulene](/wiki/File:Cyclopenta-bc-corannulene.png?lang=en)
References
- ^ Geodesic polyarenes with exposed concave surfaces Lawrence T. Scott, Hindy E. Bronstein, Dorin V. Preda, Ronald B. M. Ansems, Matthew S. Bratcher and Stefan Hagen Pure & Appl. Chem., Vol. 71, No. 2, pp. 209–219, 1999. Article
- ^ A Simple, Large-Scale Synthesis of the Corannulene System A. Sygula and P. W. Rabideau, J. Am. Chem. Soc. 122, 6323 2000. Support info Abstract
- ^ Reduction of Bowl-Shaped Hydrocarbons: Dianions and Tetraanions of Annelated Corannulenes Ivan Aprahamian, Dorin V. Preda, Mihail Bancu, Anthony P. Belanger, Tuvia Sheradsky, Lawrence T. Scott, and Mordecai Rabinovitz J. Org. Chem.; 2006; 71(1) pp 290 - 298; (Article) DOI: 10.1021/jo051949c Abstract
Notes
- Its CAS number is and its SMILES structure is C1(C=CC3=C2 C4=C(C=CC(C=C6) =C45)C=C3) =C2C5=C6C=C1.