Carbon allotrope: graphite

Abstracts, The International Conference The Electrochemistry of Carbon Allotropes Graphite, Fullerenes and Diamond , October 20-27, 1997, Cleveland, OH, USA. 

The spectacular difference between the two main carbon allotropes, graphite and diamond, as well as the recent discovery of fullerenes and nanotubes, make research in this area to be one of the most active at present. 

Figure 2 Carbon allotropes graphite (left) and diamond (right). (Reproduced with permission from sci.waikato.ac.nz/farm/ images/graphite.jpg, University of Exeter, and Getty Images, Singapore.)...

Despite many publications on carbynes, their existence has not been universally accepted and the literature has been characterised by conflicting claims and counter claims [e.g., 27-29]. This is particularly tme of meteoritic carbynes. An interesting account of die nature of elemental carbon in interstellar dust (including diamond, graphite and carbynes) was given by Pillinger [30]. Reitmeijer [31] has re-interpreted carbyne diffraction data and has concluded that carbynes could be stratified or mixed layer carbons with variable heteroelement content (H,0,N) rather than a pure carbon allotrope. 

Fig. 4. EEL spectra of (a) graphite and (b) diamond. These carbon allotropes represent different spectra sp bonding especially exhibits 7c -excitation peak lower than the o -excitation peaks (modified from ref. 16).

We can understand the differences in properties between the carbon allotropes by comparing their structures. Graphite consists of planar sheets of sp2 hybridized carbon atoms in a hexagonal network (Fig. 14.29). Electrons are free to move from one carbon atom to another through a delocalized Tr-network formed by the overlap of unhybridized p-orbitals on each carbon atom. This network spreads across the entire plane. Because of the electron delocalization, graphite is a black, lustrous, electrically conducting solid indeed, graphite is used as an electrical conductor in industry and as electrodes in electrochemical cells and batteries. Its... 

There are other allotropic forms of carbon, including graphite, Wurzite carbon... 

Carbon atoms have the ability to bond to themselves to a greater extent than those of any other element. Known as catenation, this ability gives rise to the several allotropic forms of the element. The most common form of elemental carbon is graphite, which has the layered structure shown in Figure 13.11. 

It is tempting to take the carbon insertion mechanisms to the extreme and look for the completely unsaturated carbon allotropes of graphite and diamond. Graphite has been postulated for many years but there is at present no IR evidence for it in the ISM. This is partly due to the problems of detection. The gross selection rule for an IR spectrum requires a change in dipole moment during a vibration and the... 

Abstract The past two decades have profoundly changed the view that we have of elemental carbon. The discovery of the fullerenes, spherically-shaped carbon molecules, has permanently altered the dogma that carbon can only exist in its two stable natural allotropes, graphite and diamond. The preparation of molecular and polymeric acetylenic carbon allotropes, as well as carbon-rich nanometer-sized structures, has opened up new avenues in fundamental and technological research at the interface of chemistry and the materials sciences. This article outlines some fascinating perspectives for the organic synthesis of carbon allotropes and their chemistry. Cyclo[n]carbons are the first rationally designed molecular carbon allotropes, and... 

Allotrope An allotrope is formed when an element or compound exists in more than one form. Carbon is an example of an element found in different forms (e.g., carbon black, graphite, and diamonds). Oxygen has three alio tropes monoatomic or nascent oxygen (O) diatomic oxygen (O ), the gas we breathe and triatomic oxygen (O ), which is known as ozone. 

For synthetic chemists, who are interested in the transformation of known and the creation of new matter, elemental carbon as starting material once played a minor role. This situahon changed dramatically when the family of carbon allotropes consisting of the classical forms graphite and diamond became enriched by the fullerenes. In contrast to graphite and diamond, with extended solid state stmctures, fullerenes are spherical molecules and are soluble in various organic solvents, an important requirement for chemical manipulations. 

Though Ceo has not (so far) found any major applications, the influence of C6o is now pervasive in chemistry and beyond.8 C6o is a kind of ideal nanoscale building block that can be picked up and manipulated with nanotechnological tools.9 Importantly, its curved, hollow structure has made us familiar with another view of carbon materials, different and complementary to that of flat sheets of carbon atoms in graphite. Ultimately, all the interest generated around such carbon allotropes has driven the research in the field and introduced the perhaps most notable representatives of the present nanoworld, carbon nanotubes (NTs). 

The fullerenes (Cf/i, C70 and higher molecular allotropes)la, discovered by Kroto, Smalley and coworkers in 1985lb, represent the third form of carbon, following graphite and diamond. However, it was not until 1990, when Kraschmer, Huffman and coworkerslc,ld... 

C60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in circumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature-low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented. 

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