Classification of carbon atoms

Literature data on the carbon skeleton elongation may be classified according to the number of carbon atoms added. Such a classification, although far from being ideal, is useful from the synthetic viewpoint. Scheme 2 illustrates the usefulness of a-amino acids (in particular a-amino-(3-hydroxy acids e.g., serine, threonine, and their homologues) in the synthesis of amino sugars. 

As first shown by Boehm in 1975 [41] on CDC synthesized from TaC and SiC, and later for most carbide precursors [33], the resulting carbons have type I isotherms in the Brunauer classification, which are indicative of microporous carbon having pore sizes less than 2nm and relatively high surface areas up to 2000m2/g [37,39,42], The pore size of CDC can be tailored by the selection of carbide precursors with different spatial distributions of carbon atoms in the initial carbide lattice, changing the nanotextural ordering in the CDC by varying the synthesis temperature, and posttreatment in a... 

Classification of alcohols. Alcohols are classified according to the type of carbon atom (primary, secondary, or tertiary) bonded to the hydroxyl group. Phenols have a hydroxyl group bonded to a carbon atom in a benzene ring. 

B Classification of Terpenes Terpenes are classified according to the number of carbon atoms, in units of ten. A ter-... 

The classification of conjugated systems into alternant and nonalternant ones covers compounds both with even and with odd number of carbon atoms. However, certain properties of even and odd ASs may differ. 

A common method of classification for petroleum is the PONA system (PONA is an acronym for paraffins, olefins, naphthenes, and aromatics). Paraffins are straight-chain or branched hydrocarbons in which there are no double or triple bonds between carbon atoms. Olefins are similar to paraffins, but they contain at least one multiple bond in their chemical structure. Naphthenes are saturated hydrocarbons, just like paraffins, but they incorporate a ring of carbon atoms into their chemical structure. Aromatics contain a benzene ring in their structure. 

Table 26-1). In addition, the carbon atoms may be labeled with Greek symbols, with a being adjacent to the carboxyl group and 0) being farthest away. In the A-system, fatty acids are abbreviated according to the number of carbon atoms, the number of double bonds, and the position(s) of double bond(s). For example, linoleic acid, which contains 18 carbons and two unsaturated bonds between carbons 9 and 10 and between carbons 12 and 13, could be written as Ci8 2 Using the T - or (D-system, linoleic acid would be abbreviated to Ci8 2n-6, where only the first carbon forming the unsaturated pair is written. The Geneva or systematic classification is a third system of nomenclature (Table 26-1).

Carbynes are white solids made up of carbon atoms with sp hybridization. Two main possibilities [23] exist for this Hnear structure polyine (—C=C—C=C—) and polycumulene (=C=C=C=C=) theoretical predictions and experimental evidence also point to the existence of cycHc carbynes [10]. According to a classification based on the type of bond present (Table 2.1), and also according to chronology, carbynes (rather than fuUerenes) should be considered as the third aUotropic form of carbon. Our scarce knowledge of carbynes and doubts about whether they really exist in pure form [10, 15, 26] are factors that have contributed to this erroneous interpretation. Moreover, lonsdaleite and rhombohedral graphite should be considered as polytypes rather than new structures with a different equation of state [27]. Strictly speaking, therefore, they should not be regarded as true allotropes of carbon (Table 2.1). 

Classification of monosaccharides is done by the number of carbon atoms and the types of functional groups. For example, glucose and fructose have the same chemical formula, but different structure glucose having an aldehyde (internal hydroxyl shown as -OH) and fructose having a keto group (internal double-bond O, shown as =0). 

Let us review briefly the classifications of carbon-containing compounds, particularly those of interest in atmospheric chemistry. The carbon atom has four valence electrons and can therefore share bonds with from one to four other atoms. The nature of the carbon-carbon bonding in a hydrocarbon molecule basically governs the properties (as well as the nomenclature) of the molecule. 

Figure 4.3 Classification of CNTs based on the number of graphitic layers present and the arrangement of carbon atoms in these layers.

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