Fullerene carbon numbering

The nature of the electronic states for fullerene molecules depends sensitively on the number of 7r-electrons in the fullerene. The number of 7r-electrons on the Cgo molecule is 60 (i.e., one w electron per carbon atom), which is exactly the correct number to fully occupy the highest occupied molecular orbital (HOMO) level with hu icosahedral symmetry. In relating the levels of an icosahedral molecule to those of a free electron on a thin spherical shell (full rotational symmetry), 50 electrons fully occupy the angular momentum states of the shell through l = 4, and the remaining 10 electrons are available... 

Another early suggestion was that some of the fullerene carbon atoms could be replaced by another element such as nitrogen or boron.1811 Such heterofullerenes are envisaged to have strongly altered chemical properties in comparison to the all-carbon structures.1811 For example, as the substitution number of an electronegative element such... 

By observing the number and relative intensity of 13C resonances it is possible to identify to which point group an adduct belongs. For C60, with Ih symmetry, all 60 carbon atoms are equivalent, giving rise to a single sharp line at 143.3 ppm in C6D6. Complex formation causes a reduction in symmetry, and the fullerene carbon atoms become in-... 

The C60 unit of 26a displays 52 resonances in the 13C-NMR spectrum which indicates the absence of any symmetry element in this molecule. One signal has a relative intensity of four, two signals have each a relative intensity of three and one signal has a relative intensity of two thus the number of carbon atoms sums up to 60. While two fullerene carbon atoms resonate at 63.99 (C1) and 77.50 (Ch) ppm, the other 50 signals appear in the region between 130-165 ppm. In the -NMR spectrum of 26a, the four alkylidene methyl protons gave rise to new resonances two isopropyl methyl protons Ha and Ha, isopropyl methine proton Hb, one methyl proton FF and methylene protons H- and H-. These observations support the migration of an alkylidene methyl proton to an alkylidene... 

To identify modified fullerenes a numbering system for the carbon atoms is necessary. According to the IUPAC nomenclature [209], based on the proposal of Taylor in 1993 [210], the carbon atoms are numbered as outlined for C6o and C70 in Fig. 29. 

The discovery of fullerenes, carbon molecules with geodesic structures, has prompted a number of studies, both theoretical and experimental, devoted to the possible existence of non-carbon analogues of these species [18-21]. From a theoretical point of view this discovery opens the way toward the preparation of new forms of known substances. In addition to theoretical interests, such polyhedrons could fecilitate a much more diverse chemistry than has been possible so far with carbon fullerenes. 

If the number of carbon atoms in a fullerene is n = V, then the number of edges is E =. From Euler formula F — E -I- V = 2 follows the number of faces as F = 2 -b Y Also from the Euler formula follows that in fullerenes the number of pentagons is 12 and the number of hexagons is( — lO). Thus knowing the number... 

The scope of tire following article is to survey the physical and chemical properties of tire tliird modification of carbon, namely [60]fullerene and its higher analogues. The entluisiasm tliat was triggered by tliese spherical carbon allotropes resulted in an epidemic-like number of publications in tire early to mid-1990s. In more recent years tire field of fullerene chemistry is, however, dominated by tire organic functionalization of tire highly reactive fullerene... 

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]. 

The state of research on the two classes of acetylenic compounds described in this article, the cyclo[ ]carbons and tetraethynylethene derivatives, differs drastically. The synthesis of bulk quantities of a cyclocarbon remains a fascinating challenge in view of the expected instability of these compounds. These compounds would represent a fourth allotropic form of carbon, in addition to diamond, graphite, and the fullerenes. The full spectral characterization of macroscopic quantities of cyclo-C should provide a unique experimental calibration for the power of theoretical predictions dealing with the electronic and structural properties of conjugated n-chromophores of substantial size and number of heavy atoms. We believe that access to bulk cyclocarbon quantities will eventually be accomplished by controlled thermal or photochemical cycloreversion reactions of structurally defined, stable precursor molecules similar to those described in this review. 

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