Alkanes side-chain

Electronic behavior of polysilanes in the solid state can be even more complex. The best-studied examples are (Hexyl2Si) (16) and (Pentyl2Si) (17). Compound 16 undergoes a reversible change, endothermic by 4.0 kcalmol-, at 42 °C96. Samples heated above 50 °C show Amax = 316 nm, much like that in solution, but in the low-temperature form the absorption band is shifted to 372 nm. Crystallization of the alkane side-chains is believed... 

The acrylates (fifth and sixth in the list of Figure 2) are part of a series in which the alkane side chain length was varied over a range of 1 (methyl) to 16 (hexadecyl). The experiments are described completely elsewhere (8), and include a similar series on the methacrylates one of which poly(methyl methacrylate) (PMMA), is shown as seventh in the list of Figure 2. 

It is important to keep in mind that manipulation of alkane side chains will affect polymer solubility. In a fully substituted polymer, there is good solubility, but steric interactions due to the side chains decrease conjugation. On the other hand, the unsubstituted polymer avoids these steric interactions but is insoluble. The removal of side chains along the polymer has also been shown to decrease solubility. Thus, there will likely be a balance between enhanced conjugation and good solubility. 

Elimination of Steric Clashes Between Alkane Side Chains. There are three main approaches that potentially eliminate the side chain interactions that decrease the degree of conjugation in processable polythiophenes use shorter alkane chains, control the regiochemistry of the polymer, and increase the distance between side chains along the polymer backbone. 

Thiophene/AULylthiophene Copolymers. Another class of polymers that have been prepared in an attempt to minimize the steric effects of alkane side chains are random copolymers of thiophene and an alkylthiophene.(75,77) Only scattered reports of the optical properties of these polymers are available. Hotta found that the random copolymer of 3-hexylthiophene and thiophene gave a of 440 nm in solution which compares to 434 nm for poly(3-hexylthiophene) prepared under the... 

In alkyl-substituted methacrylate polymers, an additional transition is detected ultrasonically and has also been observed using dynamic mechanical and dielectric measurements. This relaxation is associated with conformational changes of the alkane side chain (Figure 17). The motion of... 

Marchessault R H, Monasterios C J, Morin F G and Sundararajan P R (1990) Chiral poly(3-hydroxyalkanoates) an adaptable helix influenced by the alkane side-chain. Intern J Biol Macromol 12 158-165. 

The itaconic acid polymer is, in fact, really a fully protected backbone chain polymer. If you make models, what you find is that it really has a whole lot of oxycarbonyl units protecting the backbone and you have a nonpolar alkane side chain. So, in the case of the alkane side chains, when you have a very high density of these, they don t really want to intertwine with and cross over the main backbone because they re repelled. 

Monocyclic Aliphatic Hydrocarbons. Monocyclic aliphatic hydrocarbons (with no side chains) are named by prefixing cyclo- to the name of the corresponding open-chain hydrocarbon having the same number of carbon atoms as the ring. Radicals are formed as with the alkanes, alkenes, and alkynes. Examples ... 

Otherwise, radicals having the free valence(s) in the side chain are named in accordance with the rules for alkanes, alkenes, or alkynes. 

The prefix iso is used loosely to denote branched alkanes or alkenes that have one or more methyl groups only as side chains. 

Alkanes can be simultaneously chlorinated and chlorosulfonated. This commercially useful reaction has been appHed to polyethylene (201—203). Aromatics can be chlorinated on the ring, and in the presence of a free-radical initiator alkylaromatic compounds can be chlorinated selectively in the side chain. King chlorination can be selective. A patent shows chlorination of 2,5-di- to 2,4,5-trichlorophenoxyacetic acid free of the toxic... 

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

The molecular ion intensity decreases with increased branching, therefore the molecular ion peak may be nonexistent. The loss of 15 Daltons from the molecular ion indicates a methyl side chain. The mass spectra of branched alkanes are dominated by the tendency for fragmentation at the branch points, and hence are difficult to interpret. 

Because the types of carbon-carbon bonds present in the molecule tend to dominate its properties, an aliphatic hydrocarbon is first classified as an alkane, alkene, or alkyne. Then the longest chain of carbon atoms is used to form the root of the name. Other hydrocarbon groups attached to the longest chain are named as side chains. 

The names of straight-chain alkanes are given in Table 18.1 they all end in -ane. Name a hydrocarbon side chain as a substituent by changing the ending -ane to -yl (as in the last two columns in Table 18.1). 

IR and Raman spectroscopic studies on films and powders of PDHS indicate that the hexyl side chains are crystallizing into a hydrocarbon type matrix (40). This is indicated by the presence of a number of sharp characteristic alkane bands which become dramatically broadened above the transition temperature. Similar changes are observed for n-hexane below and above the melting point. CPMAS 29Si NMR studies on PDHS also show that the rotational freedom of the side chains increases markedly above the transition temperature (41,42). All of the spectral evidence... 

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

The rhodium-catalyzed borylation of alkanes is applied to regiospecific functionalization of polyolefines.165,165a The reaction of polypropylenes (atactic, isotactic, and syndiotactic) with B2pin2 in the presence of Cp Rh( 74-C6Me6) catalyst at 200 °G affords the borylated polymers, which are treated with basic hydrogen peroxide in a mixture of THF and H20 to oxidize the boronate esters to the corresponding alcohols (Scheme 20). The hydroxylated polymers contain 0.2-1.5% hydroxymethyl side-chains. 

---