Carbon, covalent bond types

Organic peroxides are another type of cross-linking agents. Vulcanization by means of peroxides is a free radical process that leads to the formation of carbon-carbon covalent bonds between chains. Below we show a diagram of the process ... 

Unsaturated polyesters have reactive double carbon-carbon covalent bonds that can be cross-linked to form thermosetting materials. The polymers are usually cross-linked with vinyl-type molecules such as styrene, using a peroxide to generate free radicals (see Fig. 15.3). Commercial resins are viscous... 

Polar covalent bonds can be regarded as having some degree of ionic character, and the distinction between ionic and covalent bond types is sometimes hard to make. Some compounds have clear examples of both types of bonding simultaneously. Thus CaC03 has well-defined carbonate ions... 

The sharing of electron pairs in carbon—carbon covalent bonds may be as a single bond or with double bonds. Single bonds have complete freedom of rotation whereas double bonds are shorter and do not allow free rotation. Therefore, the type of covalent bond is important for such electrical properties as polarization and relaxation time. 

The compounds of carbon and silicon with hydrogen would be expected to be completely covalent according to these models, but the dhectionality of the bonds, which is towards the apices of a regular tetrahedron, is not explained by these considerations. Another of Pauling s suggestions which accounts for this type of directed covalent bonding involves so-called hybrid bonds. 

A large body of experimental evidence confirms that covalent bonds have characteristic distances depending on bond type. Carbon-carbon single and double bond lengths are around 1.54A and 1.32A, respectively, while partial double bond distances, e.g., in benzene, are about 1.40A. 

The DNA monomers are each completed by a phosphate group, —O—P032, covalently bonded to carbon atom 5 of the ribose unit to give a compound called a nucleotide (28). Because there are four possible nucleoside monomers (one for each base), there are four possible nucleotides in each type of nucleic acid. 

There are distinct structural types of organic compounds containing metals and metalloids. The first contain covalent carbon-metal bonds and are strictly organometallic compounds, for example, the alkylated compounds of Hg, Sn and Pb, and of Li, Mg, and A1 (and formerly Hg), which have been extensively used in laboratory organic synthesis, and A1(C2H5)3 that is a component of the... 

Two structures are possible for the interaction of aromatic hydrocarbons with acids.270 In the a-structures a covalent bond is established between the acidic reagent and a particular carbon atom of the benzene ring. The a-structures are essentially classical carbonium ions. In the -structures a non-classical bond is established, not to any particular atom, but to the -electron cloud in general. It is quite likely that both types of structure are represented by actual examples. Thus m-xylene interacts more strongly with hydrogen chloride than does o-xylene, but the difference between the two hydrocarbons is much more pronounced when their interactions with a boron trifluoride-hydrogen fluoride mixture are compared. This is readily understandable... 

There are several, separate types of interaction in III both covalent bonds and dipoles. Induced dipoles involve a partial charge, which we called <5+ or S, but, by contrast, covalent bonds involve whole numbers of electrons. A normal covalent bond, such as that between a hydrogen atom and one of the carbon atoms in the backbone of III, requires two electrons. A double bond consists simply of two covalent bonds, so four electrons are shared. Six electrons are incorporated in each of the rare instances of a covalent triple bond . A few quadruple bonds occur in organometallic chemistry, but we will ignore them here. 

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