Carbon catenation

Of all of the elements of the Periodic Table, only neighboring carbon and boron share the properties of self-bonding (catenation) and the support of electron-delocalized structures based upon these catenated frameworks. Carbon catenation, of course, leads to the immense field of organic chemistry. Boron catenation provides the nido-, arachno-, and /i p/io-boranes, which may be considered as the borane equivalents of aliphatic hydrocarbons, and the discrete families of c/oso-borane derivatives which bear a for nal resemblance to the aromatic hydrocarbons, heterocycles, and metallocenes. Aside from these analogies, boron and carbon chemistries are also important to each other through their extravagant ability to mix m ways not available to other element-pairs. Thus, the conflux of boron and carbon chemistries effectively provides an element-pair for exploitation in a variety of novel ways. 

Apart from carbon, catenation does not occur to any great degree in the chemistry of the other elements. Si and Ge do form hydrides that might be compared with the lighter hydrocarbons, but they are not as stable. Catenation in these elements involves the formation of Si-Si and Ge-Ge covalent bonds, which are longer and therefore weaker than C-C bonds. 

As in carbon chemistry, catenation is an important feature in silicon and germanium chemistry. However, unlike carbon catenated compounds, main chain, and these... 

All Group IV elements form tetrachlorides, MX4, which are predominantly tetrahedral and covalent. Germanium, tin and lead also form dichlorides, these becoming increasingly ionic in character as the atomic weight of the Group IV element increases and the element becomes more metallic. Carbon and silicon form catenated halides which have properties similar to their tetrahalides. 

Carbon atoms bond to each other to form chains, a process known as catenation. Open chains ... 

On the other hand, formates are less stable. This seems to be related to the H-CO-S atomic catenation in which 2 is an oxygen or chlorine atom. Nevertheless, with esters, the presence of a base as well as a high temperature and pressure are necessary. In the presence of sodium methoxide in a small quantity (0.5%), at 100°C and under 70 bar, methyl formate decomposes according to the reaction below the violent release of carbon oxide creates a dangerous overpressure in the apparatus ... 

Because of the tendency of sulfur toward catenation, solutions containing sulfides react with sulfur to give polysulfides, which can be represented as SnJ (see Chapter 15). Sulfides of the group IA and IIA metals can also be produced by reducing the sulfates with carbon at high temperature. 

Carbon atoms have the ability to bond to themselves to a greater extent than those of any other element. Known as catenation, this ability gives rise to the several allotropic forms of the element. The most common form of elemental carbon is graphite, which has the layered structure shown in Figure 13.11. 

In the right part of the Table hydrides having covalent characteristics are observed. For the elements of the last groups several covalent hydrogen compounds are known numerous compounds are given by B, C, Si, Ge, N, P, O, S, Se. In the usual ambient conditions, as it is well-known, the carbon chemistry is especially rich of hydrides (that is of several series of hydrocarbons). In this class of compounds more or less complex molecules and structures are found the catenation (chainforming) tendency is a characteristic shown by several elements in this portion of the Periodic Table. 

The chains in the polymers discussed so far consist of isochains of catenated carbon atoms. However, many polymers such as the polyacetal— polyoxymethylene (POM), Delrin—have other atoms in addition to the carbon atoms in the polymer chain. As shown by the abbreviated segmental formula for the polyacetals... 

Since most polymers consist of covalently bonded catenated carbon atoms, they are nonconductors of heat and electricity. This property is essential when these polymers are used as electric insulators, but is a nuisance when the stored electrostatic charges collect dust or cause electromagnetic interference (EMI). 

Aromatic cyclic chains are more stable than aliphatic catenated carbon chains at elevated temperatures. Thus linear phenolic and melamine polymers are more stable at elevated temperatures than polyethylene, and the corresponding cross-linked polymers are even more stable. In spite of the presence of an oxygen or a sulfur atom in the backbones of polyphenylene oxide (PPO), polyphenylene sulfide (PPS), and polyphenylene sulfone, these polymers are... 

The polymer molecules described previously were catenated carbon chains with various pendant groups. The polymer molecules described in this chapter have other atoms in the polymer chain, either in addition to or in place of the carbon atoms. 

Of the elements which participate in catenation (chain formation) in their elementary states, only carbon retains the property in its compounds to any great extent. The relatively high strength of the single covalent bond between two carbon atoms gives rise to such a large... 

In both papers two key ideas were set forth — 1) the idea of the tetravalent carbon atom, and 2) the concept of catenation (that carbon atoms could form chains). Both papers also stated explicitly, for the first time, what became known as the chemical stracture of a compound, and the idea that the properties of the compoimds depended on the properties and arrangement of their component atoms, rather than the more complex (and less well defined) radicals. The appearance of these papers also resulted in a polemical interchange over priority that left Couper a broken man, and boosted Kekule (with the help of Wurtz, amongst others) to the top echelons of organic chemistry in Emope (5). 

The tendency of atoms of certain elements to form chains with themselves (homoatomic catenation) or in alternation with other atoms (heteroatomic catenation) is of extreme importance in chemistry. The immense subject of organic chemistry and, indeed, life as we know it depend on the special ability of carbon to catenate from the chemical engineering standpoint, catenation and the associated ability to form molecular rings and cages provide opportunities to make materials of desired mechanical, electrical, thermal, chemical, or catalytic properties. 

Sulfur is usually only divalent, unless oxidized, and its catenation chemistry is therefore more limited and less familiar than that of carbon. Solid a-sulfur contains very stable eight-membered crown like rings, Ss,... 

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