Carbon covalent bonding

The most important enzymes involved in monosaccharide biosynthesis are those which will synthesize a carbon-to-carbon covalent bond and, in reverse, cause fission of this bond. It is becoming increasingly clear that... 

Figure 10-4 shows the hybridization that occurs in ethylene, H2C=CH2. Each carbon has sp2 hybridization. On each carbon, two of the hybrid orbitals overlap with an s-orbital on a hydrogen atom to form a carbon-to-hydrogen covalent bond. The third sp2 hybrid orbital overlaps with the sp2 hybrid on the other carbon to form a carbon-to-carbon covalent bond. Note that each carbon has a remaining p-orbital that has not undergone hybridization. These are also overlapping above and below a line joining the carbons. 

These three hydrocarbons all have the same molecular formula. We can see their different structural features by highlighting the carbon framework in two dimensions. Easy-to-draw stick structures that use lines for all carbon—carbon covalent bonds can also be used. 

The trimethylamine adduct of aluminum hydride (alane) has been of recent interest as a precursor for the chemical vapor deposition (CVD) of aluminum metal1 and aluminum gallium arsenide thin films.2 Because of the absence of aluminum-carbon covalent bonds in the precursor, carbon incorporation in the resulting films can be suppressed significantly. In addition, the deposition temperature can be lowered. 

The final R-factor and structural parameters exceed the standards described in Section I and attest to the high quality of this model. Atom locations are precise to an average of 0.34 A. about one-fifth of a carbon-carbon covalent bond length. The plot of temperature factors shows greater variability and range for side-chain atoms, as expected, and shows no outlying values. The model defines the positions of all amino-acid residues in the protein. 

The atmospheres of these planets convect, of course. To survive on Jupiter, any hypothetical life based on molecules containing carbon-carbon covalent bonds would have to avoid being moved by convection to positions in the atmosphere where they are not stable. This is, of course, not impossible. Even on Earth, life in the oceans must avoid being moved by convection from its particular habitable zone. Sagan and Salpeter presented a detailed discussion of what might be necessary for a floater to remain stable in the jovian atmosphere.25... 

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... 

We can consider a partially ionic sigma bond as an already partially broken bond. An organometallic bond, for example, has electrons that are very available. Conversely, a carbon-carbon covalent bond is completely covalent its electrons reside in a very stable sigma bonding orbital and are not available. The main exception to this is the C-C bonds of cyclopropane, which are destabilized by ring strain, and thus are more reactive. 

Here, q represents the relative resonance stabilization conferred on the new radical by R2 and e may be represented as the charge induced by the radical R2 or Ri on either of the carbon atoms forming the new carbon—carbon covalent bond in the transition state. Originating from Eqs. [1.2] and [1.3], the following monomer reactivity ratios were computed for the mixture of styrene(l)-m-DVB(2)-p-DVB(3) 2 = 0.45, f2i=0.60, ri3 = 0.14. 

In all eases, Al atoms arc found to react with the conjugated systems by forming new Al-carbon covalent bonds. As a consequence, the carbon atoms involved in the bonding adopt an p hybridization. The n electron conjugation is dramatically perturbed and the corresponding wavcfunction delocalization, which constitutes the basis for the electronic properties of these materials, is significantly reduced in polytmcs or even disrupted in polythiophenes. ... 

In more general terms, the thermal decomposition of coal is a complex process (Stein, 1981 Solomon et al., 1992). Activation energies determined by experimental techniques indicate that the decomposition rate(s) is (are) controlled by the scission of carbon-carbon covalent bonds and the like (POutsma, 1987). In fact, the concepts that bond scission during coal pyrolysis can be induced by other means (McMillen et al., 1989) or can be influenced by cross-linking are sound and deserve consideration in the light of coal complexity and the potential interference of the primary products with one another as well as with the vestiges of the original coal. 

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. 

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