Corannulene molecule

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

At this point, we notice that the corannulene molecule provides an ideal model for addressing a very interesting problem how much aromaticity is lost when a molecule is distorted from the strongly aromatic planar structure to a nonplanar structure The answer to this question must be a key to the possible existence of superaromaticity in the C60 molecule (5). 

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 ... 

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]. 

As with corannulene, conventional routes for the preparation of 28 have been unsuccessful, due no doubt to the strain associated with this molecule nevertheless. 

Other molecules in which benzene rings are forced out of planarity are corannulene (20),45 (also called 5-circulene), 7-circulene (21),46 22,47 and 2348 (see also p. 161). 

It should be noted, however, that planarity had not been excluded for corannulene until the X-ray analysis was performed. The molecule is a non-alternant hydrocarbon because it contains an odd-membered ring. Hence, the it-electron density distribution cannot be uniform in the ground state. One of such polar structures is the double Hiickel aromatic structure 66, c consisting of peripheral 14n and central 6ir systems. The contribution of resonance as shown in 6 c will be at its maximum when the whole molecule is planar like coronene (8). Notwithstanding, the planar corannulene will have huge angle strain. If we assume that all C-C bonds are 1.40 A in length and the... 

We removed the top and bottom radialene units of the fullerene molecule to generate [10]cyclophenacene as described above. An alternative view of [60]fullerene may generate hemispherical bowl-shaped aromatic systems [lc, 37] for instance, fused corannulene C (C30H12, Chart 2.1), can be identified as half of fullerene [38]. 

The metastable, 2-D packing motif presented by some Pcs adsorbed on Ag(l 11) has also prompted the utilization of such ensembles as templates for the organization of complementary guest molecules such as fullerenes [193] or corannulenes [194], giving rise to the formation of two-component, 2-D architectures. More recently, a similar approach has been used to prepare a surface-supported, three-component system. In fact, the immersion of an Au substrate into a solution containing both a ZnPc and a Zn porphyrin led to the formation of a highly ordered, 2-D arrangement of both Pc and porphyrin which can act as a bimolecular chessboard toward the supramolecular assembly of a third component (i.e., C6o fullerene) which is selectively trapped in the open spaces (Fig. 25) [195],... 

It has been found that all of the reviewed stable fullerenes include corannulene (Fig. 2, a) and indacene (Fig. 2, b) - substructures typical for the most stable fullerenes C6o and C70. There are perylene (Fig. 2, c) and coronene (Fig. 2, d) substructures present in a structure of some higher fullerenes. The presence of three or more coronene substructures essentially destabilizes the higher fullerene molecules. Anyway, the more the size of a fullerene cage, the weaker this effect that compensates by increasing of fullerene sphere dimension. The analysis of electronic structure of stable (isolated) fullerenes also show that all stable fullerenes have a closed shell and their molecules are characterized by a rather uniform distribution of pentagons along a fullerene sphere. 

Incorporation of five-membered rings into the polyhexagon sheet creates curvature in the PAH, as seen in corannulene. Larger polyaromatic C30H12 bowls, (110 and 111), have been recently synthesized by Rabideau et al. [146,147] and Scott et al. [148]. The largest molecule yet synthesized in this family, C36H12... 

A first theoretically substantiate paper on C o vvas published by E. Osawa in 1970. He let himself be inspired by his son s soccer ball while reflecting on superaromatic Jt-systems and postulated an analogous structure with icosahedral symmetry for the Ca)-molecule, predicting its stabiUty from Hiickel calculations. He saw that corannulene, synthesized shortly before by Barth and Lawton, had to be a partial structure of that cage (Figure 2.1). His pubhcations as well were granted due attention only after the experimental discovery of fullerenes. 

Condensed polycyclic benzenoid aromatic hydrocarbons are customarily regarded as planar molecular structures because of the geometrical constraints of carbon atoms in a state of sp2 hybridization. A well-known exception is the class of compounds called the helicenes (18) for which the nonbonded overlap of two terminal benzenoid rings in a cata-condensed structure, as in structure 1, forces a molecule into a nonplanar helical structure. A second exceptional class of compounds is related to corannulene (2) and other an-nulenes of this type (19, 20). In corannulene, strain associated with the pericondensed five- and six-membered rings requires adoption of a bowlshaped structure (20, 21). For both structures 1 and 2 the aromatic character of the benzenoid rings is retained to an appreciable extent. 

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