Preferable fullerenes

It has been known [6-10] that C6o fullerene reacts easily with proton donors and accepts electrons to form anion radicals. Thus, one might expect the preferred fullerene transformations in electrolysis to be related to the fullerene reactions on the cathode. Anion radical transformations can occur both on the surface and in the solution. It has been known that fullerene forms solvates [16] with many solvents (Sol), in particular with toluene. With electrons (D) in the donor medium, two competitive processes can proceed in the reaction system (donor-C6o-solvent)... 

Preferable-Fullerene Theorem. For every even vertex count v < 70 there exists at least one preferable fullerene, and the sole smaller preferable fullerene is the truncated icosahedron with v = 60. 

Again, the proof is constructive. Further, all fullerenes so far experimentally obtained in macroscopic quantities fall into the class of this theorem—and the two smallest such preferable fullerenes (at v = 60 and v = 70) corresponding to the two species most readily experimentally obtained. 

Arc discharge [25] is initially used for producing C60 fullerenes. Nanotubes are produced by arc vaporization of two carbon rods placed in a chamber that is filled with low pressure inert gas (helium, argon). The composition of the graphite anode determines the type of CNTs produced. A pure graphite anode produce preferably MWNT while catalyst (Fe, Co, Ni, Y or Mo) doped graphite anode produces mainly SWNT. This technique normally produces a complex mixture of components, and requires further purification to separate the CNTs from the soot and the residual catalytic metals present in the crude product. 

In should be noted that the same problem exists for both other photosensitizers and other methods for decontamination of the blood and its components (e.g. absorption) (Mohr, 2000). The use of fullerenes is to be preferred to the use of photoactive dyes because the former are water-soluble components. Due to its insolubility in water, fullerene may be easily removed from the liquid phase after the procedure of decontamination. 

Example Fullerene soots as obtained by the Huffman-Kratschmer synthesis of fullerenes can be characterized by positive- as well as negative-ion LDI. [115] The LDI-TOF spectrum of such a sample exhibits fullerene molecular ion signals well beyond m/z 3000 among these, Ceo and 070" are clearly preferred (Fig. 10.11). Furthermore, such samples provide experimental carbon-only isotopic patterns over a wide mass range (Chap. 3.2.1). 

The bowl-shaped hydrocarbons give an opportunity to study convex versus concave preferences for complex formation which relates to the interest in endo-hedral complexes of fullerenes. 

There have been several developments in this area since this manuscript was prepared. The heat of combustion of corannulene was determined by microbomb combustion calorimetry and its gas-phase enthalpy of formation was estimated at 110.8 kcal/mol. All anionic oxidation states of corannulene were observed by optical absorption, EPR, and NMR spectroscopies. More support for the an-nulene-within-annulene model of the corannulene tetraanion was presented. An alternative pyrolysis route to corannulene was reported, as well as some attempts toward the synthesis of bowl-shaped subunits of fullerenes. And in contrast with previous semiempirical studies," ab initio calculations predicted a general concave preference for the metal cation binding to semibuckminsterfullerene 2%. ... 

Fullerenes can also be obtained by pyrolysis of hydrocarbons, preferably aromatics. The first example was the pyrolysis of naphthalene at 1000 °C in an argon stream [58, 59], The naphthalene skeleton is a monomer of the Cjq structure. FuUerenes are formed by dehydrogenative coupUng reactions. Primary reaction products are polynaphthyls with up to seven naphthalene moieties joined together. FuU dehydrogenation leads to both Cjq as well as C7Q in yields less than 0.5%. As side products, hydrofuUerenes, for example CjqHjj, have also been observed by mass spectrometry. Next to naphthalene, the bowl-shaped corannulene and benzo[k]fluoranthene were... 

The isolated dimethyldihydro[60]fullerenes are a mixture of the 1,2- and 1,4-iso-mers (1.4 1) (Scheme 2.2). Of the 23 possible regioisomers of 50(0113)2 the 1,2-and 1,4-isomers are predicted to be the most stable, with the heat of formation of the 1,4-isomer being a little bit larger than that of the 1,2-isomer [87]. The electron density in the intermediate CgolCHj) is calculated to be largest at C-2 (25%) followed by C-4/C-11 (9% each). This also suggests that the second electrophilic attack of Mel should be preferred at C-2, even if it is taken into account that there are two sites available for a 1,4-addition mode. 

MNDO or ab initio calculations (Table 5.3). Further confirmation for the preference of 1,2-addition was established by ab initio calculation of the C-H bond energy in hydrogenated fullerenes [35]. Hybrid density functional theory using the B3LYP functional with the 6-31 G(d,p) basis set leads to the bond energies shown in Table 5.3. The most stable bond is found in 1,2 adducts with a bond energy of 2.86 eV, followed by a bond energy of 2.69 eV in 1,4-adducts. All the other addition patterns such as 1,3 addition or addition to a [5,6] bond lead to less stable C-H bonds (Table 5.3). 

Like CgQ most of the characterized higher fullerenes can be considered as electron-deficient polyenes. They exhibit similarities in their chemical behavior [1-3]. Preferred primary addition reactions are, for example, addition of nucleophiles, as well as cycloadditions at the bonds adjacent to two six-membered rings ([6,6]-bonds). The most important difference from the chemistry of Cgg is due to the less symmetrical cages of the higher fullerenes, which exhibit a broad variety of bond environments with unequal reactivity towards addition reactions. Consequently... 

Bond a is the most polarized double bond within the fullerene framework and the preferred reaction site for a subsequent attack. 

The conjugation in the molecular wire may be disrupted or modulated to create systems with different properties. For example, a porphyrin Ceo donor-acceptor system linked with a conjugated binaphthyl unit, has a preference for the atropi-somer where the fullerene unit is closer to the porphyrin system, thus increasing the through space interactions [82]. The charge transfer process on a dyad containing a crown ether in the linker structure can be modulated by complexation/ decomplexation of sodium cations [83] but even more interesting is the construction of supramolecular systems where the donor and acceptor moieties are... 

---