Carbon allotrope

Carbon exists in different allotropic forms, viz. Fullerene (OD, a zerodimensional carbon), carbon nanotube (ID, a one-dimensional carbon), graphene (2D, a two-dimensional carbon), graphite (3D, a three-dimensional carbon) and diamond (3D, a three-dimensional carbon). All the above forms except diamond (which bears sp hybridized carbons) have a structural similarity having sp hybridized carbon. 

---

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... 

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. 

Carbon nanotubes (CNTs) as well as fullerenes are splendid gift brought to the Earth from the red giant carbon stars in the long-distant universe through the spectroscopy. Moreover, those belong to new carbon allotropes of the mesoscopic scale with well-defined structures. In particular, CNTs are considered to be the materials appropriate to realise intriguing characteristics related to the mesoscopic system based on their size and physicochemical properties. 

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... 

This article summarizes efforts undertaken towards the synthesis of the cyclo[ ]carbons, the first molecular carbon allotropes for which a rational preparative access has been worked out. Subsequently, a diversity of perethynylated molecules will be reviewed together, they compose a large molecular construction kit for acetylenic molecular scaffolding in one, two and three dimensions. Finally, progress in the construction and properties of oligomers and polymers with a poly(triacetylene) backbone, the third linearly conjugated, non-aromatic all-carbon backbone, will be reviewed. 

The following is a comprehensive smwey of the chemistry of macrocycles comprised entirely of phenyl and acetylenic moieties. Although over fom" decades old, this area of research has come into its own just in the last few years. Widespread interest in the field has been spurred by recent discoveries utilizing these compoimds as ligands for organometallic chemistry, hosts for binding guest molecules, models of synthetic carbon allotropes, and precursors to fullerenes and other carbon-rich materials. This review will discuss the preparation of a tremendous variety of novel structm-es and detail the development of versatile synthetic methods for macro cycle construction. 

Table 2 Restricted Hartree-Fock energies (Hartrees) for Ceo and C70 and their muon adducts. AE is the difference in energy between the carbon allotrope and its adduct. In all cases, except where indicated by f, only the six carbon atoms in the immediate vicinity of the muon have had there positions optimised, f means that a full geometry optimisation has been carried out. The type specifies the defect and for C70 is identified in Table 1. is the spin density at the muon in atomic units (and the hyperfine coupling constant in MHz). JMuon constrained to lie in equatorial plane. indicates geometry not fully optimized.

Donaldson, K. et al. (2010) Asbestos, carbon nanotubes and the pleural mesothelium a review of the hypothesis regarding the role of long fibre retention in the parietal pleura, inflammation and mesothelioma. Particle and Fibre Toxicology, 7, 5. Hirsch, A. (2010) The era of carbon allotropes. Nat. Mater., 9 (11), 868-871. Tasis, D. et al. (2006) Chemistry of carbon nanotubes. Chemical Reviews, 106 (3), 1105-36. 

In 1985, the story of carbon allotropes took a dramatic turn with the discovery of C60, which resulted in a new type of carbon structure, called the fullerenes (Kroto et al., 1985). This discovery earned the 1996 Nobel Prize in chemistry for Harold Kroto, Robert Curl, and... 

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... 

From Fullerenes to Novel Carbon Allotropes Exciting Prospects for Organic Synthesis... 

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... 

Following the discovery of a bulk fullerene preparation process in 1990, the covalent chemistry of these carbon allotropes has developed at a phenomenal pace. Frontier orbital (LUMO) and tether-directed functionalization concepts have been successfully applied to the regio- and stereoselective preparation of multiple covalent adducts of C60. These have found increasing applications in the construction of functional supramol-ecules. More recently, the sequence of Bingel reaction - retro-Bingel reaction has provided an elegant access to isomerically pure higher fullerenes and, in particular, to pure carbon enantiomers. 

Keywords Carbon Allotropes m Fullerenes m Cyclocarbons m Nanomaterials m Advanced Materials m Optical Activity... 

Aspects of Covalent Fullerene Chemistry Regioselective Multiple Functionalization, Optically Active Carbon Allotropes, and Electroluminescent Devices (LEDs)... 

Novel Fullerene-Based Carbon Allotropes and Total Synthesis of C60... 

For a review, see F. Diederich, Y. Rubin, Synthetic Approaches Towards Molecular and Polymeric Carbon Allotropes , Angew. Chem Int. Ed, Engl 1992, 31, 1101-1123. 

---