Theoretical investigation of carbon nets and molecules

Publisher Summary This chapter discusses systems that are formed from carbon atoms. Adopted as first classification are the dichotomy infinite/finite systems—that is, macromolecule versus molecule; as a second criterion, systems are discussed in terms of hybridization, using the well-known types sp, sp 2 , sp 3 although these are only first approximations for dicoordinated, tricoordinated,and tetracoordinated atoms, because the exact hybridization is determined by the valence angles. The chapter explains the infinite planar nets of sp 2 -hybridized carbon atoms. Graphite's delocalization is associated with high electrical and thermal conductivity within the graphene plane. Single crystals have conductivities about 200 times higher within the molecular planes than across them. The strong anisotropy, because of covalent bonding within the honeycomb lattice and to Van der Waals forces in the orthogonal direction, leads to linear compressibilities 104–105 times larger in the latter direction. The opacity and black color of graphite are because of the large aromatic chromophore. Graphite is the thermodynamically favored allotropic form of elemental carbon, so it is possible to gradually convert diamond into graphite on heating at 1000° at normal pressure in the absence of air. The other planar infinite lattices and tridimensional infinite lattices with sp 2 -hybridized carbon atoms are discussed in the chapter. There are details of diamond's three-dimensional infinite network, other systems with sp 3 -hybridized carbon atoms, and holes bordered by heteroatoms within the diamond lattice. There is discussion on infinite nets with both sp 2 - and sp 3 -hybridized carbon atoms—the local defects in the graphite lattice and the diamond lattice. In the chapter, systems with regularly alternating sp 2 /sp 3 -hybridized carbon atoms are also discussed. The chapter describes the infinite chains of sp-hybridized carbon atoms, molecules with sp 2 -hybridized carbon atoms—fullerenes, nanotubes and capsules, carbon cages and nanotubes including oxygen, nitrogen, or boron heteroatoms—and molecules with sp- and sp 2 -hybridized carbon atoms.