Fullerene rings

Other linked structures. These include fullerene rings, linked ball-and-chain dimers,and an increasing variety of other forms. Examples are shown in Figure 8-17. 

These include fullerene rings/ dimers (Figure 8.24c and 8.24d)," and chiral fullerenes." Endofullerenes ... 

The same characteristic patterns in H chemical shifts are found in fulleroid derivatives such as 23— 28 or 29—33,2 ° 2i7 where either a proton or a methyl group is placed above a fullerene ring (Figure 15). In the case of the methyl groups, the effects appear to be somewhat attenuated (for Instance, Ad between 30 and 31 is only 1.9 ppm), certainly due to the averaging of the three methyl protons, only one of which will be located in close proximity to the ring at a given time. 

Fully conjugated cyclopolyynes, so-called cyciocarbons, constitute another class of carbon modifications besides diamond, graphite, and the recently discovered fullerenes (see section 5.6). Syntheses of these unstable rings might be possible by mild elimination, extrusion, or... 

The field of fullerene chemistry expanded in an unexpected direction in 1991 when Sumio lijima of the NEC Fundamental Research Laboratories in Japan discovered fibrous carbon clusters in one of his fullerene preparations This led within a short time to substances of the type portrayed in Figure 11 7 called single-walled nanotubes The best way to think about this material IS as a stretched fullerene Take a molecule of Ceo cut it in half and place a cylindrical tube of fused six membered carbon rings between the two halves... 

The significance of the magic number 32 found in the experiment may also be stated in a different manner. If a cluster containing Ba and a fuUerene molecule will be stable and, thus, result in a clearly discernible structure in the mass spectra every time there is exactly one Ba-atom situated on each of the rings of the ful-lerene molecule, this property might be used to count the rings of a fullerene. Of course, such a proposal has to be verified using other fullerenes, for example, C70 which is available in sufficient quantity and purity for such an experiment. 

Fig. 3. Mass spectra of photoionized QgCa (top) and C7oCa) (bottom) the lower axis is labeled by the number of metal atoms on the fullerene molecule. The peaks at x = 32 for C Ca and x = 37 for C7oCa , correspond to a first metal layer around the fullerenes with one atom located at each of the rings. The edges at x = 104 and x = 114, respectively, signal the completion of a second metal layer.

With C70 at the center of the cluster, we observed the completion of layers al x = 37, 114, and 251. For completion of the observed three layers around C70, each layer requires 5 atoms more than the corresponding layer around C o- The arrangement of atoms in the first layer is again obvious place one atom above each of the 37 rings of the fullerene. 

All of the carbon atoms in buckminster-fullerene are equivalent and are sp -hybridized each one simultaneously belongs to one five-membered ring and two benzene-like six-membered rings. The strain caused by distortion of the rings from coplanarity is equally distributed among all of the carbons. 

Addition reactions — The fullerenes Ceo and C70 react as electron-poor olefins with fairly localized double bonds. Addition occurs preferentially at a double bond common to two annelated 6-membered rings (a 6 6 bond) and a second addition, when it occurs is generally in the opposite hemisphere. The first characteriz-able mono adduct was [C6oOs04(NC5H4Bu )2]. formed by reacting Cgo with an excess of OSO4 in 4-butylpyridine. The structure is shown in... 

Cycloalkenones and/or their derivatives can also behave as dienic partners in the Diels-Alder cycloaddition. It is well documented [41] that cyclic acetals, for example, can interconvert with ring-opened enol ether forms, in a reversible manner the latter compounds can then be trapped by various dienophiles. Thus dienes 119 and 120 reacted with [60]-fullerene (Ceo) at high pressure, affording highly thermally stable products [42] (Scheme 5.16). Ketones 123 and 124 could be directly obtained by cycloaddition of enol forms 121 and 122 of 2-cyclopen-ten-and 2-cyclohexen-l-one, respectively. 

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