Bond , 16-25 with carbon hydrocarbons

Alternating polarity may also occur in aliphatic molecules, but is generally present to a lesser extent than in the aromatic series. The resonance in the non-substituted hydrocarbons between the forms C and C C+ will be negligible on the introduction of an atom e.g, chlorine, which forms a partially ionic bond with carbon, however, alternating polarity can be induced and resonance between the forms X and XI will occur. 

As you can see in Figure 22-6, cyclic hydrocarbons such as cyclohexane are represented by condensed, skeletal, and line structures. Line structures show only the carbon-carbon bonds with carbon atoms understood to be at each vertex of the structure. Hydrogen atoms are assumed to occupy the remaining bonding positions unless substituents are present. 

To picture what polymers are, it is helpful to start with small synthetic polymers. You use such polymers every day. Plastics, synthetic fabrics, and nonstick surfaces on cookware are polymers. The unsaturated hydrocarbon ethylene, C2H4, is the monomer of a common polymer used often in plastic bags. The monomers are bonded together in a chemical reaction called polymerization (puh lih muh ruh ZAY shun). As you can see in Figure 15, the double bond breaks in each ethylene molecule. The two carbon atoms then form new bonds with carbon atoms in other ethylene molecules. This process is repeated many times and results in a much larger molecule called polyethylene. A polyethylene molecule can contain 10,000 ethylene units. 

Fluorine forms a very tight bond with carbon, and fluorocarbon chains are more stable and more inert than hydrocarbon chains. Fluorocarbon polymers are waxy, water-repellent, solvent-repellent, electrically insulating substances. A fluorocarbon plastic (Teflon) has come into use, in the 1960s, as a film to cover frying pans, which then no longer require fat for frying. 

All bulky substituents attached to carbon atoms of the pyranose ring (hydroxyl, carboxyl and acetamide groups) and a glycosidic bond with connected hydrocarbon residues occupy an equatorial and sterically more favourable position. The hydrogen atoms are in less sterically favourable axial positions (Figure 4.2), which explains why part of the molecule... 

Carbon can also form multiple bonds with other carbon atoms. This results in unsaturated hydrocarbons such as olefins (alkenes), containing a carbon-carbon double bond, or acetylenes (alkynes), containing a carbon-carbon triple bond. Dienes and polyenes contain two or more unsaturated bonds. 

Alkenes are hydrocarbons that contain a carbon-carbon double bond A carbon-carbon double bond is both an important structural unit and an important func tional group m organic chemistry The shape of an organic molecule is influenced by the presence of this bond and the double bond is the site of most of the chemical reactions that alkenes undergo Some representative alkenes include isobutylene (an industrial chemical) a pmene (a fragrant liquid obtained from pine trees) md fame sene (a naturally occurring alkene with three double bonds)... 

Our experience to this point has been that C—H bonds are not very acidic Com pared with most hydrocarbons however aldehydes and ketones have relatively acidic protons on their a carbon atoms pA s for enolate formation from simple aldehydes and ketones are m the 16 to 20 range... 

Chlorine reacts with saturated hydrocarbons either by substitution or by addition to form chlorinated hydrocarbons and HCl. Thus methanol or methane is chlorinated to produce CH Cl, which can be further chlorinated to form methylene chloride, chloroform, and carbon tetrachloride. Reaction of CI2 with unsaturated hydrocarbons results in the destmction of the double or triple bond. This is a very important reaction during the production of ethylene dichloride, which is an intermediate in the manufacture of vinyl chloride ... 

This reaction has often reached explosive proportions in the laboratory. Several methods were devised for controlling it between 1940 and 1965. For fluorination of hydrocarbons of low (1—6 carbon atoms) molecular weight at room temperature or below by these methods, yields as high as 80% of perfluorinated products were reported together with partially fluorinated species (9—11). However, fluorination reactions in that eta involving elemental fluorine with complex hydrocarbons at elevated temperatures led to appreciable cleavage of the carbon—carbon bonds and the yields invariably were only a few percent. 

Steric Factors. Initially, most of the coUisions of fluorine molecules with saturated or aromatic hydrocarbons occur at a hydrogen site or at a TT-bond (unsaturated) site. When coUision occurs at the TT-bond, the double bond disappears but the single bond remains because the energy released in initiation (eq. 4) is insufficient to fracture the carbon—carbon single bond. Once carbon—fluorine bonds have begun to form on the carbon skeleton of either an unsaturated or alkane system, the carbon skeleton is somewhat stericaUy protected by the sheath of fluorine atoms. Figure 2, which shows the crowded hehcal arrangement of fluorine around the carbon backbone of polytetrafluoroethylene (PTFE), is an example of an extreme case of steric protection of carbon—carbon bonds (29). 

The single-monomer route (eq. 5) is preferred as it proves to give more linear and para-linked repeat unit stmctures than the two-monomer route. Other sulfone-based polymers can be similarly produced from sulfonyl haUdes with aromatic hydrocarbons. The key step in these polymerisations is the formation of the carbon—sulfur bond. High polymers are achievable via this synthesis route although the resulting polymers are not always completely linear. 

In a class of reahstic lattice models, hydrocarbon chains are placed on a diamond lattice in order to imitate the zigzag structure of the carbon backbones and the trans and gauche bonds. Such models have been used early on to study micelle structures [104], monolayers [105], and bilayers [106]. Levine and coworkers have introduced an even more sophisticated model, which allows one to consider unsaturated C=C bonds and stiffer molecules such as cholesterol a monomer occupies several lattice sites on a cubic lattice, the saturated bonds between monomers are taken from a given set of allowed bonds with length /5, and torsional potentials are introduced to distinguish between trans and "gauche conformations [107,108]. 

An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Alkyne carbon atoms are sp-hybridized, and the triple bond consists of one sp-sp a bond and two p-p tt bonds. There are relatively few general methods of alkyne synthesis. Two good ones are the alkylation of an acetylide anion with a primary-alkyl halide and the twofold elimination of HX from a vicinal dihalide. 

We have already remarked that ethane is a member of a family of compounds called the saturated hydrocarbons. This term identifies compounds that contain only carbon and hydrogen in which all bonds to carbon are single bonds formed with hydrogen or other carbon atoms. They occur in chains, branched chains, and cyclic structures. 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

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