Bonding carbon family

Many hydrate cavities have analogs (1) in the clathrasils in which SiC>2 replaces water as a host molecule (Gerke and Gies, 1984) and (2) in the Buckminsterfullerene (covalently bonded carbon cavities) family (Curl and Smalley, 1991). Even with these analogous structures providing estimates of other cavities, for hydrate unit crystals there is the additional restriction that the cavities must be packed to fill space. 

Based on the extension by the repetition of three kinds of C-C bonds to infinite molecules, we may define carbon families, consisting of diamond, graphite, fullerenes, and carbynes [1], In each family, the structure shows characteristic diversities representative structures are listed in Figure 2.2. The detailed diversity in structure will be explained in the following sections for each family. Most structures in each family are thermodynamically metastable, and the family is represented by the allotrope name. In Figure 2.2, some possibilities to accept foreign species are also illustrated. 

Solids based on sp hybridization, although subject of intense experimental efforts, seem to be the most elusive of the different carbon families [5]. The existence of linear chains of carbon atoms linked by alternating single and triple bonds (polyyne) or double bonds (polycumulene) with stabilizing molecular complexes at the end of the chains, has been recognized in interstellar molecular clouds and can be artificially produced by different chemical routes [6-8],... 

Silicon and germanium have been found to form clathrate-type host lattices in which guest species are alkali atoms. The host lattices are exactly the same as those of type 1 and II hydrates "" (see 16.2.2). They are formed by atoms of only one kind, which are bonded together by strongly covalent forces, as in the Si or Ge diamond structures. The Si—Si or Ge—Ge bond lengths are of the same order of magnitude as in classical Si or Ge with the bond angles 109°28 which characterizes the tetrahedral sp hybridization of the carbon family. 

Because carbon compounds are so numerous, it is convenient to organize them into families that have structural similarities. The simplest class of organic compounds is the hydrocarbons, compounds composed of only carbon and hydrogen. The key structural feature of hydrocarbons (and of most other organic substances) is the presence of stable carbon—carbon bonds. Carbon is the only element capable of forming stable, extended chains of atoms bonded through single, double, or triple bonds. 

Protonated saturated hydrocarbons contain a carbon atom which is formally 5-coordinate. There are insufficient electrons to describe such a carbocation by a classical structure and it is necessary to invoke a 3-centre 2-electron bond. This family of non-classical alkonium ions are generally known as carbonium ions. Removal of H2 from an alkonium ion leaves a carbocation containing a 3-coordinate carbon. These trivalent alkyl cations are known as carbenium ions. The interrelation between the two classes of carbocations is shown for the parent ions in equation 2. 

Modification of the SH-group of 6-mercaptopurine by suitable substituents results in strong activation of the thioether bonds. A family of substances (Fig. 1) has been used to attach a covalent label to amino acid side chains, preferentially to the —SH group. The reaction proceeds to a cleavage of the aromatic thioether with liberation of a thiophenol. The carbon-6 of the purine is bound to the amino acid side chain although, in some cases, the nitrophenyl moiety is transferred onto the protein. 

How the Type of Bonding in an Element Affects Physical Properties 434 How Bonding Changes in the Carbon Family s Compounds 436 Highlights of Carbon Chemistry 436 Highlights of Silicon Chemistry 438... 

All the families in the first group are nucleophiles, because of their electron-rich carbon-carbon double or triple bonds. And because double and triple bonds have relatively weak TT bonds, the families in this group undergo addition reactions. Since the first species that reacts with a nucleophile is an electrophile, the reactions that the families in this group undergo are more precisely called electrophilic addition reactions. 

Pristine graphene is a two-dimensional sp bonded carbon nanostructure [2, 30]. Most significantly however, graphene is a key derivative of carbon and originates from a large family of fullerene nanomaterials where it is the essential building block for many of the allotropic dimensionalities that have significant and widespread use as electrode materials [2, 30]. 

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