Isomers, fullerene

In addition to the most abundant fullerene, namely [60]fullerene, a number of higher fullerenes have also been isolated and characterized, including [70] (point group D . ), chiral [76] (point group Dj), the D and Cj isomers... 

I he results of their calculations were summarised in two rules. The first rule states that at least one isomer C with a properly closed p shell (i.e. bonding HOMO, antibonding I. U.MO) exists for all n = 60 - - 6k (k = 0,2,3,..., but not 1). Thus Qg, C72, Cyg, etc., are in lhi-< group. The second rule is for carbon cylinders and states that a closed-shell structure is lound for n = 2p(7 - - 3fc) (for all k). C70 is the parent of this family. The calculations Were extended to cover different types of structure and fullerenes doped with metals. 

The higher mass fullerenes (C76, Cs4), with multiple isomers of different shapes, also crystallize in the fee structure at room temperature, with an fee lattice constant which is approximately proportional to where n is the number of carbon atoms in the fullerene [53]. 

Recently, there has been considerable interest in fullerene derivatives. Finding the lowest energy isomer among a variety of choices of attachment is always an interesting and important question. In C50, all carbons are equivalent, but there are two types of C-C bonds ... 

C))]. A copiously illustrated atlas of fullerenes elaborating and enumerating the numbers and structures of all possible fullerenes and fullerene isomers C as a function of n up to high n has recently been published. 

In 2000, it was proposed that the regioselectivity of the [3 + 2] cycloaddition of fullerenes could be modified under microwave irradiation. Under conventional heating, N-methylazomethine yhde and fullerene-(C7o) gave three different isomeric cycloadducts because of the low symmetry of C70 vs. Ceo. Using microwave irradiation and o-dichlorobenzene as a solvent, only two isomers were obtained, the major cycloadduct 114 being kinetically favored (Scheme 39) [75]. The same authors had previously reported the 1,3-dipolar cyclo addition of pyrazole nitrile oxides, generated in situ, to Geo under either conventional heating or microwave irradiation. The electrochemical characteristics of the cycloadduct obtained with this method made this product a candidate for photophysical apphcations [76]. 

The fullerene C o was used as the Unking agent for the synthesis of (PCHD-fc-PS)6 and (PS-fc-PCHD)6 star-block copolymers [154], The polymers were then aromatized with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, DDQ, in 1,2-dichlorobenzene to yield the corresponding copolymers containing poly(l,4-phenylene) blocks. In order to achieve high 1,4-isomer contents and to avoid termination reactions, the polymerization of CHD was conducted in toluene at 10 °C without the presence of any additive to yield products with low molecular weights. Coupling of the PCHD-fo-PSLi to C60... 

Y. Nishida, A. Mizuno, H. Kato, A. Yashiro, T. Ohtake, and K. Kobayashi, Stereo- and biochemical profiles of the 5-6- and 6-6-junction isomers of a-D-mannosyl [60]fullerenes, Chem. Biodivers., 1 (2004) 1452-1464. 

Fullerenes Cycloaddition reactions are very popular for functionalization of fullerenes. Such reactions of fullerenes are compiled and discussed in detail in Reference 253. During the last 10 to 15 years, several communications appeared concerning [3 + 2] cycloaddition of nitrile oxides to fullerene C60- Nitrile oxides, generated in the presence of C60, form products of 1,3-cycloaddition, fullerene isoxazolines, for example, 89. The products were isolated by gel permeation chromatography and appear by and 13 C NMR spectroscopy to be single isomers. Yields of purified products are ca 30%. On the basis of 13C NMR, structures with Cs symmetry are proposed. These products result from addition of the nitrile oxide across a 6,6 ring fusion (254). 

G. Sun, Fullerenes identihcation of isomers based on nuclear magnetic resonance spectra, in Dekker Encyclopedia of Nanoscience and Nanotechnology, (eds J. L. Atwood and J. W. Steed), Marcel Dekker, New York, 2004, p. 1223. 

The solid-state reaction of C o with one equivalent of C70 in the presence of 4-aminopyridine under the HSVM conditions for 30 min afforded a cross dimer of these two fullerenes, C130 (5), albeit in a low yield (3%) [27]. The NMR and UV-vis spectral analyses of the product indicated that only an isomer having a Cgo cage attached to the 1,2-junction bond of C70 was selectively produced by this reaction, in addition to C120 (3). 

Fig. 3 STM images of fraction A containing fullerene trimers 6a-6d and fraction B containing 6e, together with the calculated energy relative to that of equatorial isomer...

In another nomenclature recommendation it was suggested that fullerenes be named in the same way as annulenes, for which the number of C-atoms is indicated in square brackets in front of the word [4]. For fullerenes the number of C-atoms is accompanied by the point group symmetry and by the number of the isomer (using capital Roman) in cases were there are more than one. This is especially important for higher fullerenes. Thus, for Buckminsterfullerene the full description is... 

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