Fullerene-spheroid chirality

Figure 1.1. Elow diagram for the facile classification of different types of fullerene-spheroid chirality in fullerene derivatives.

C. Examples for the Configurational Description of the Different Classes of Chiral Fullerene Spheroids... 

Although not a perfect fullerene spheroid, another chiral carbon allotrope, C119, was isolated in the form of a 13C-enriched sample from the thermolysis of Ci2o0.74 On grounds of the obtained 13C NMR spectra as well as molecular modeling, Kratschmer and co-workers proposed a C2-symmetric, peanut-shaped structure consisting of two fullerene-like C58 units bridged by three sp3-C-atoms, two of which are symmetry-equivalent.74... 

Figure 1.26. Double Bingel addition to C70 leads to an achiral top) and two inherently chiral (center and bottom) addition patterns. Combination of each of the latter with chiral ester moieties affords two diastereoisomeric pairs of enantiomers. The enantiomers of each pair were prepared separately by addition of either (R,R) or (S, -configured malonates to C70, and all stereoisomers were isolated in pure state. The black dots mark intersections of the C2-symmetry axis with the [70]fullerene spheroid. Next to the three-dimensional representations, constitution and configuration of the addition patterns are shown schematically in a Newman type projection along the Cs-axis of C70. Of the two concentric five-membered rings, the inner one corresponds to the polar pentagon closest to the viewer, and the attached vertical line represents the bond C(l)-C(2) where the first addition occurred. The functionalized bonds at the distal pole depart radially from the outer pentagon.

Fig. 2. Flow diagram allowing a facile classification of spheroid chirality in fullerene adducts...

In the case of the second most favored C(5)-C(6)-adduct (type P) which often accompanies the C(l)-C(2) mono-adduct in product mixtures [27], a f 2v -symmetrical addend again affords a single product isomer (e.g. 7-10, Fig. 5), whereas addition of a Q-symmetrical addend leads to a pair of enantiomers [( )-ll. Fig. 5]. In the latter case, a chiral addition pattern is created on the fullerene spheroid. Being due only to differences in nature, sequence, or steric arrange-... 

Derivatives of achiral parent fullerenes in which the functionalization creates a chiral addition pattern on the spheroid, regardless of the addends being identical or different, have an inherently chiral functionalization pattern. The derivatives of chiral parent fullerenes automatically have an inherently chiral functionalization pattern. 

Fig. 1. A selection of higher fullerenes for which certain to confident structural assignments were possible. The chiral carbon spheroids are represented by a single enatiomer only in the case of D2-C76,the configuration as well as a characteristic CD (circular dichroism) maximium of the shown enantiomer are indicated...

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... 

The fullerene derivatives at the focus of the present review result from exohedral addition to the larger carbon spheroids [27] with particular emphasis being given to the structural aspects related to chirality. However, a number of other higher fullerene derivatives, including chiral structures as well, is worth being briefly mentioned. 

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