Chiral fullerenes structures

A proposed structural description of chiral fullerene derivatives using a bond-labeling algorithm eventually also relies on the helicity of the fullerene numbering schemes.110... 

Figure 6 The spectroscopically cxjnfitmed cage structures of the first three fullerenes to be isolated inmacroscopic amounts A-Ceo, Dsh-Cjo, and the chiral fullerene D2-C76...

New carbon modifications, which consist of discrete polyhedral molecules, have been intensively investigated since the early 1990 s. The structures of these fullerenes range from the highly symmetrical buckminsterfullerenes, C50, to the chiral fullerenes, 7, to larger tubular or carbon particles built up of onionscale-shaped molecules. Possible applications, such as the manufacture of superconducting alkali metal-doped fullerenes or their utilization as a support for catalysts, are being developed, but are not yet market ripe. 

After the potential occurrence of chiral fullerenes and nanotubes could be inferred from the structural principles of fullerenes [35-37], these carbon spheroids became of practical interest for the first time with the isolation and characterization of D2-symmetrical Cyg by Diederich and coworkers [1]. Obeying the IPR (isolated pentagon rule) and having a closed electronic shell with a fully occupied HOMO (highest occupied molecular orbital), its structure had been theoretically predicted shortly before to be the only stable form of [76]fuUerene... 

According to structural criteria of chiral fullerene derivatives, three different types of core functionalization patterns can be distinguished [34] (Fig. 2) ... 

Carbon nanotubes (CNTs) are members of the Fullerene structural family. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene (Fig. 3.8). The manner in which these sheets are connected to form tubes at specific and discrete ( chiral ) angles and the combination of the angle and radius decides the nanotube properties for example, whether the individual nanotube exhibits metal or semiconductor like behaviour. The values of n and m are used not only for the chirality or twist but also to draw a line between metallic and semiconducting nanotubes. In other words, chirality in turn affects the conductance, density, lattice structure, and certain other properties of the nanotube. A nanotube is considered metallic if the value m is divisible by three. Otherwise, the nanotube is semiconducting. 

M. Terrones, G. Terrones, H. Terrones, Structure, chirality, and formation of giant icosahedral fullerenes and spherical graphitic onions, Struct. Chem., vol. 13, pp. 373-384, 2002. 

The photochemical addition of cyclic 1,3-diones such as dimedone, 1,3-cylohexandione 62, or their respective silyl enol ethers leads to the formation of two fused furanylfullerenes, (1) achiral 63 and (2) chiral 64 [244], The latter having an unusual bis-[6,5] closed structure. In the initial step of this reaction, [2 + 2] photocycloaddition across a [6,6] bond to form cyclobutanols or the corresponding TMS ethers is involved (Scheme 26). Oxidation with 02 yields in the formation of the radical 65a. Cleavage to 66a followed by cyclization gives furanyl radical 67a. H abstraction by 102 or a peroxy radical finally leads to product 63. In competition, formation of fullerene triplets by absorption of a... 

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