Corannulene

as well as the vibrational frequencies from an ab initio study (Bakowies and Thiel 1991). Cyclic conjugation in drculenes, including corannulene ([5]drculene), has been studied (Gutman and Lee 1993). Corannulene has eleven Kekule structures (Bergan, Cyvin BN and Cyvin 1987 Brendsdal and Cyvin 1989 Cyvin SJ, Brendsdal et al. 1991). 

Corannulene has recently attracted new interest among organic chemists. Two new syntheses have been reported (Scott, Hashemi, Meyer and Warren 1991 Borchardt et al. 1992), and the bowl—to-bowl inversion has been discussed (Scott, Hashemi and Bratcher 1992 Borchardt et al. 1992). 

Considerable interest is attached to cydacenes (cyclic acenes, d particularly to 

Sessions 1985), e.g. C gH g [12]beltene, are partial-hydrogenated analogues of cydacenes. Beltenes have also been called colunmenes (Angus and Johnson 1988). Some theoretical works with predictions on cydacenes are available (Ege and Vogler 1974 Kivelson and Chapman 1983). 

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Examine the geometry of planar corannulene. Are all of its six-membered rings the same If so, draw a Lewis structure whieh best represents the molecule. If not, draw one or more Lewis structures as appropriate. 

Aeeording to your Lewis structure(s) and to the actual geometry of the molecule, is the bonding in planar corannulene fully delocalized (as in benzene), or are some CC bonds long and some short Do your results support the notion that planar corrannulene is resonance stabilized Explain. 

Buckminsterfullerene (Cm or Buckyball ) is structurally related to corannulene. In which molecule would you expect 7U-orbital overlap be more effective Explain. How many chemically unique carbons are there in C6o Measure CC bond distances. How many unique distances are there Is each benzene fully delocalized or is one resonance contributor more important than the other ... 

To investigate the basis set effect in connection with geometric strain in BF, we have performed calculations with and without d-type functions on corannulene. The d-functions improve the binding with about 10 kcal/mol per C-atom in C20H10 the corresponding improvement in coronene (C24H 2) 8 kcal/mol. 

Figure 10 (left). The Buckminsterfullerene molecule. Figure 11 (right). The Corannulene molecule C2oHio ... 

If both ethylene subunits of a l,3-hexadien-5-yne derivative are members of benzene entities, the cycloaromatization, caused by flash vacuum thermolysis, may give rise to bowl-shaped molecules such as corannulene or semibuckminsterfullerene. However, in those cases, the initial step is not a Hopf cydization but an isomerization of the ethynyl to a vinylidenecarbene group [125]. 

From the assemblies of fused five- and six-membered rings identifiable on the surface of 1, corannulene (8) is the smallest fragment that retains a bowl-shaped conformation. However, there are other known hydrocarbons that adopt bowl (or... 

The preceding section indicated the importance of corannulene as the smallest member of the family of bowl-shaped, polynuclear aromatic hydrocarbons modeling the surface of buckminsterfullerene. Surprisingly, despite its obvious significance in relationship to the theory of aromaticity, 8 had not attracted the attention of chemists prior to the first report of its synthesis in 1966." As Barth and Lawton noted ... to the time of our first report, it appears this structure had neither adoriied the jacket or end cover of any book nor served as a symbol of an international symposium. More than that, corannulene does not appear to have been suggested in the chemical literature prior to 1966. 

Two years later, Craig and Robinson attempted an alternative synthesis of 8 with a more symmetrical pathway starting from derivatives of fluoranthene. Cycliza-tion of fluoranthene-7,10-diacetic acid 14 was attempted to produce diketone 15, expected to enolize to the dihydroxycorannulene 16. Unfortunately, several attempts at cyclization failed, including anhydrous hydrofluoric acid, concentrated sulfuric acid, and polyphosphoric acid. Friedel-Crafts cyclization of the corresponding acid chloride of 14 with aluminum or stannic chloride was similarly unsuccessful. However, although Craig and Robinson were not successful, they developed a convenient synthesis of 7,10-disubstituted fluoranthenes which turned out later to be of premium importance in a new, successful synthesis of corannulene. 

The decisive break came in 1991 when Scott and co-workers reported the formation of corannulene from 7,10-diethynylfluoranthene 19 under flash vacuum pyrolysis (FVP) conditions. The critical features of this approach appear to be the high temperature employed (900-1000 °C) and the gas-phase conditions. The high temperature provides energy for drastic fluctuations in 8 away from its equilibrium geometry, allowing the reactive centers to come close enough to form the new bonds while the gas-phase conditions prevent polymerization (although some polymeri-... 

An alternative synthesis of corannulene, also involving a pyrolysis, was reported by Siegel and co-workers (Scheme 4), The tetrabromide may be directly pyro-lyzed to corannulene, or it may be converted to a bis-sulfone where extrusion of SO2 produces a mixture of 8 along with its di- and tetrahydro derivatives, and 5,6-dimethy 1-benzo [g/ir] fluoranthene. 

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