Hydrocarbons aromatic, fullerenes

Thermodynamic parameters of the ideal-gas hydrogenation reactions for hydrocarbons and fullerene C60 are presented in Table 4.5. The enthalpies of C60 hydrogenation are within (-59 to -86) kJ per mol of H2 (A//"/n). These values are closer to similar values for aromatic hydrocarbons (-68 -f -69 kJmob1) than to those for alkenes and cycloalkenes (-110 5- -119 kJmob1). This fact is probably due to conjugation of double bonds in C60 in spite of non-aromaticity of this compound. The symmetryless hydrogenation entropies ASH /n are close for hydrocarbons and C60 (Table 4.5). 

The results given indicate the electrochemical method for the synthesis of nanostructured carbon materials to be promising. In the reaction space, dissipative self-assembly of carbon compounds takes place by the action of electric discharges. In this case, structures of new type can be formed, which are transitional between polycyclic aromatic hydrocarbons and fullerenes, nanotubes. 

Poater, J., Eradera, X., Duran, M. and Sola, M. (2003a) An insight into the local aromaticities of polycyclic aromatic hydrocarbons and fullerenes. Chem. Bur. /., 9, 1113-1122. 

Whitaker, K.W. and Sepaniak, M.J., Nonaqueous packed capillary electrokinetic chromatographic separations of large polycyclic aromatic hydrocarbons and fullerenes, Electrophoresis, 15, 1341, 1994. 

There may also be larger aromatic hydrocarbons and fullerenes. 

Herod, A.A., Stokes, B.J., Hancock, R, Kandiyoti, R., Parker, J.E., Johnson, C.A.F., John, R, Smith, G.R (1994) Laser-desorption mass spectrometry of standard polynuclear aromatic hydrocarbons and fullerenes. J. Chem. Soc. Perkin, 2,499-506. 

The Structure of Benzene 407 The Stability of Benzene 409 Bonding in Benzene 410 Substituted Derivatives of Benzene and Their Nomenclature 412 Polycyclic Aromatic Hydrocarbons 414 Fullerenes, Nanotubes, and Graphene 416-417 Physical Properties of Arenes 416... 

The main use of this reaction is for the synthesis of bowl-shaped polycyclic aromatic hydrocarbons and fullerenes [325], Exploring the boundaries of these reactions resulted in the synthesis of compounds of different geometry, tt-electron structure, aromaticity, and with the presence of heteroatoms [324]. Various cross-conjugated enediynes exert anionic cycloaromatization to form fulvene and fulvalene anions and even heterocycles. In accordance with the concept of aromaticity, the anionic Bergman type cyclization is preferred to the classical Bergman cycloaromatization of linear enediynes. This anionic cyclization differs considerably from the classical Bergman cyclization and related cycliza-tions, as well as from other dianionic cyclizations [326]. 

The main reason to mention perfect Clar structures is to draw the attention of readers to different definitions used here by Fowler and Pisanski, differ ent classifications of Clar cages by Flocke, Schmalz, and Klein, and different definitions of Clar structures of fullerenes as we have outlined at the beginning of this section. Upon closer examination, we expect readers to agree at our approach is the only one that truly extends the spirit of the jt-aro-matic sextets of Clar from benzenoid hydrocarbons to fullerenes. That does not make the alternative approaches, which are equally legitimate, less worthy, as each of them serves its own purposes — but readers should be alerted in advance and should be spared possible confusion due to use and promotion of the name of Clar in several different conceptual connections. Observe that in our definition of the Clar structure of fullerene, only hexagonal faces can be the site of aromatic jr-sextets, but that is not the case in the approach of Fowler and Pisanski, where pentagonal faces play a role similar to that of hexagonal faces. 

The interstellar medium may also appear as dark clouds that absorb starlight. The densities are several 10 particles cm . In such clouds polycyclic aromatic hydrocarbons (PAHs), fullerenes, carbon-chains, diamonds etc. are found. 

Physical properties of Fullerene C q. It does not melt below 360°, and starts to sublime at 300° in vacuo. It is a mustard coloured solid that appears brown or black with increasing film thickness. It is soluble in common organic solvents, particularly aromatic hydrocarbons which give a beautiful magenta colour. Toluene solutions are purple in colour. Sol in (5mg/mL), but dissolves slowly. Crysts of C o are both needles and plates. 

Reduction of fullerenes to fullerides — Reversible electrochemical reduction of Ceo in anhydrous dimethylformamide/toluene mixtures at low temperatures leads to the air-sensitive coloured anions Qo" , ( = 1-6). The successive mid-point reduction potentials, 1/2, at -60°C are -0.82, -1.26, -1.82, -2.33, —2.89 and —3.34 V, respectively. Liquid NH3 solutions can also be used. " Ceo is thus a very strong oxidizing agent, its first reduction potential being at least 1 V more positive than those of polycyclic aromatic hydrocarbons. C70 can also be reversibly reduced and various ions up to... 

Fullerenes. Fullerenes are a family of aromatic hydrocarbons, based on the parent buckminsterfullerene (108 that have a variety of very... 

Polycyclic aromatic hydrocarbons such as fluoranthrene or Cso-fullerene are structures of great interest A straightforward entrance to analogues and partial structure, respectively, has now been developed by de Meijere and coworkers [89], using a combination of a Suzuki and a Heck-type coupling. Thus, reaction of 1,8-dibromophenanthrene 6/1-166 and obromphenylboronic acid 6/1-167 employing 20 mol% of the Pd° catalyst led to 6/1-168 and 6/1-169 in 54% yield as a Id-mixture (Scheme 6/1.45). 

Now and then, projectiles from outer space cause excitement and surprises, as in January 2000, when a meteorite impacted the frozen surface of Lake Targish in Canada. It was a new type of C-chondrite with a carbon concentration of 4-5%, and probably came from a D-type asteroid (Hiroi et al., 2001). More exact analysis of the Targish meteorite showed the presence of a series of mono- and dicarboxylic acids as well as aliphatic and aromatic hydrocarbons (Pizzarello et al., 2001). Aromatic compounds and fullerenes were detected in the insoluble fraction from the extraction this contained planetary helium and argon, i.e., the 3He/36Ar ratio was... 

It is exciting to study the progression of the chemical and physical properties of these systems as a function of their size to determine at what stage (if any) these hydrocarbons begin to behave like the all-carbon cages. That is, these curved polynuclear aromatics may serve as models for the fullerenes. 

Corannulene is the simplest example within the class of polynuclear aromatic compounds with curved surfaces that are related by carbon framework to the i fullerenes. These aromatic hydrocarbons possess bowl-shaped geometries, consist... 

The chemistry of curved, polynuclear aromatic hydrocarbons holds great promise due, in part, to the rampant interests in fullerenes. Of special interest, of course, is their relationship to the fullerenes, and these compounds should serve as good models in many ways since the curvature of the systems already known matches that of buckminsterfullerene, at least at the point of maximum curvature. 

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... 

If solutions of CgQ in aromatic hydrocarbons are treated with Lewis acids, such as AICI3, AlBrj, FeBrj, FeClj, GaClj or SbClj, then a fullerylation of aromatics takes place (Scheme 8.11) [66, 88, 90, 91], In this case, the Lewis acid serves as a catalyst and increases the electrophilicity of the fullerene. Mixtures of polyarylated fullerenes are obtained. Depending on the reaction conditions and the aromatic used for the fullerylation, up to 16 aryl groups are covalently bound to the fullerene core [66, 88,... 

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