Planar carbon networks

The principle of building these planar carbon networks can also be extended to the third dimension in a manner similar to the construction of ful-lerenes from planar graphite sheets Thus, fullere-... 

Because the bisulfate anions occupy spaces between the planes of the graphite layers, they will separate the layers more than they are separated in pure graphite. The conduction between layers will be reduced. The conduction within the layers, however is enhanced because the partial oxidation produces some empty spaces in the delocalized molecular orbitals, which extend over the graphite sheet. The presence of these empty spaces makes it easier for the electrons to migrate through the solid along the planar carbon networks. 

It should be noted that the surface curvature of the carbon network exerts a profound impact on the reactivity of the fullerene core. The most striking consequence is the pyramidalization of the individual carbon atoms. Influenced by the curvature, the sp hybrids, which exist in truly 2-dimensional planar carbon networks, adopt a sp hybridization with p-orbitals that posses a s-character of 0.085 (19). Accordingly, the exterior surface is much more reactive than planar analogues, and becomes comparable to those of electron deficient polyolefines. This, in turn, rationalizes the high reactivity of the fullerene core towards many photolytically generated carbon- and heteroatomic-centered radicals (20). 

More important, tire surface curvature of tire carbon network exerts a profound impact on tire reactivity of tire fullerene core [6, 7]. In tliis context, tire most striking consequence emerges from tire pyramidalization of tire individual carbon atoms. Influenced by tire curvature, tire sp hybrids which exist in tmly two-dimensional planar... 

The most ordered surface waters are those around charged side chains or in surface crevices. Occasionally those crevices can be very deep, such as the active site pocket in carbonic anhydrase, which extends about 15 A in from the surface, with a network of water molecules (Lindskog f al., 1971). The well-ordered waters at the protein surface are usually part of an approximately tetrahedral (but sometimes planar trigonal) network of hydrogen bonds to the protein and to other waters. An example from rubredoxin is shown in Fig. 60. 

Figure 13-1 Planar all-carbon networks 45 and 46 derived from tetraethynylethene.

Scheme 13-10 Preparation of perethynylated dehydroannulene precursors to planar all-carbon networks.

The final carbonization process will be represented by a two dimensional planar graphite network and the polymerization of acenaphthylene, which is ideally shaped with the essential reactivity to cross-link in two directions [93,94], gives zethrene a graphite structure without vacancies ... 

Non-graphitic carbons arc all varieties of solids consisting mainly of the element carbon with two-dimensional long-range order of the carbon atoms in planar hexagonal networks, but without any measurable crystallographic order in the third direction (c-direction) apart from more or less parallel stacking. 

Fundamentally, this is due to the two features of the CNT structurally, the atomic planarity of graphene at 0 K and chemically, the nonpolar nature of the carbon network. 

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... 

In diamond, carbon is sp hybridized and forms a tetrahedral, three-dimensional network structure, which is extremely rigid. Graphite carbon is sp2 hybridized and planar. Its application as a lubricant results from the fact that the two-dimensional sheets can slide across one another, thereby reducing friction. In graphite, the unhybridized p-electrons are free to move from one carbon atom to another, which results in its high electrical conductivity. In diamond, all electrons are localized in sp3 hybridized C—C cr-bonds, so diamond is a poor conductor of electricity. 

A glance at the structure of graphite, illustrated in Fig. 1, reveals the presence of voids between the planar, sp -hybridized, carbon sheets. Intercalation is the insertion of ions, atoms, or molecules into this space without the destruction of the host s layered, bonding network. Stacking order, bond distances, and, possibly, bond direction may be altered, but the characteristic, lamellar identity of the host must in some sense be preserved. 

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