Hydrocarbons chains and rings

Coal A solid consisting of a tighdy bound network of hydrocarbon chains and rings. 

The fat-soluble vitamins—A, D, E, and K—can be stored in the fatty tissues of the body (especially the liver). They have nonpolar hydrocarbon chains and rings that are compatible with nonpolar oils and fats. It is important to store enough fat-soluble vitamins, but not too much because excesses are not excreted and can be toxic. 

Although the structures shown in Figure 2.5 are diverse, they all share a common characteristic. This similarity is the preponderance of hydrocarbon chains and rings so that lipid molecules largely resemble hydrocarbons. Their hydrocarbon-like molecules make lipids soluble in organic solvents. 

Hydrocarbon chains and rings bond length alternation in finite molecules... 

Unsaturated long-chain hydrocarbon molecules with their extended ir-electron system are suitable for bridging the gap between quantum chemistry and solid-state theory. A simple step-potential model of the nearly free 7T electron coupled to the lattice distortions is presented. The geometry of the molecule is obtained by requiring self-consistency between bond length and 7r-electron density in the middle of each bond. This quantum-mechanical model has no free parameter and leads to a satisfactory description of unsaturated hydrocarbon chains and rings and of defect states in rran.y-polyacetyl-ene called solitons, such as kinks, polarons, bipolarons, and excitons. 

The ability of C to catenate (i.e. to form bonds to itself in compounds) is nowhere better illustrated than in the compounds it forms with H. Hydrocarbons occur in great variety in petroleum deposits and elsewhere, and form various homologous series in which the C atoms are linked into chains, branched chains and rings. The study of these compounds and their derivatives forms the subject of organic chemistry and is fully discussed in the many textbooks and treatises on that subject. The matter is further considered on p. 374 in relation to the much smaller ability of other Group 14 elements to form such catenated compounds. Methane, CH4, is the archetype of tetrahedral coordination in molecular compounds some of its properties are listed in Table 8.4 where they are compared with those of the... 

What Are the Key Ideas The large numbers of different hydrocarDons arise from the ability of carbon atoms to form long chains and rings with one another the types of carbon-carbon bonds that are present give the hydrocarbons characteristic properties. 

Scientists classify hydrocarbons as either aliphatic or aromatic. An aliphatic hydrocarbon contains carbon atoms that are bonded in one or more chains and rings. The carbon atoms have single, double, or triple bonds. Aliphatic hydrocarbons include straight chain and cyclic alkanes, alkenes, and alkynes. An aromatic hydrocarbon is a hydrocarbon based on the aromatic benzene group. You will encouter this group later in the section. Benzene is the simplest aromatic compound. Its bonding arrangement results in special molecular stability. 

Kurtz and co-workers [11], for example, discuss the relation between Rd of hydrocarbons and molecular descriptors such as the number of carbon atoms, Nq, in the molecule, the number of chain and ring carbons, the number of side chains, and the number of double bonds. 

Figure 7.2 shows the overall processes involved in a phase I reaction. Normally a phase I reaction adds a functional group to a hydrocarbon chain or ring or modifies one that is already present.4 The product is a chemical species that readily undergoes conjugation with some other species naturally present in the body to form a substance that can be readily excreted. Phase I reactions are of several types, of which oxidation of C, N, S, and P is most important. Reduction may occur on reducible functionalities by addition of H or removal of O. Phase I reactions may also consist of hydrolysis processes, which require that the xenobiotic compound have a hydrolyzable group. 

Hydroxylation is the attachment of -OH groups to hydrocarbon chains or rings. Aliphatic hydroxylation of alkane chains can occur on the terminal carbon atom (-CH3 group or co-carbon) or on the C atom next to the last one (co-1 -carbon) by the insertion of an O atom between C and H, as shown below for the hydroxylation of the side chain on a substituted aromatic compound ... 

In aldehydes the carbonyl group, C=0, is attached to a C and H atom at the end of a hydrocarbon chain, and in a ketone it is bonded to two C atoms in the middle of a hydrocarbon chain or ring. The hydrocarbon portion of aldehydes and ketones may consist of saturated or unsaturated straight... 

The hydrocarbon framework is made up of chains and rings of carbon atoms, and it acts as a support for the functional groups. 

C bonds readily with itself to fonn chains and rings and forms a multitude of compounds with hydrogen (hydrocarbons). See chapter 18. 

Alkanes are the simplest hydrocarbons. The carbons in an alkane can be arranged in a chain or a ring, and both chains and rings can have branches of other carbon chains attached to them. Alkanes that have no branches are called straight-chain alkanes. Methane, CH4 ethane, C2H6 propane, CjHg and butane, C4H10 are all common fuels. Their structural formulas show that each differs from the next by an increment of — CH2—. 

Another possibility is that the ring structure may have long hydrocarbon chains attached at the comers so that they stand up at one side. These chains provide the hydrophobic component and the polarizable ring stmcture provides the hydrophilic moiety. There are studies with porphyrins bearing four long hydrocarbon chains and whose hydrophilic moieties are associated with the ring stmcture [80, 81]. However, these materials did not lead to the formation of ordered multilayers. The same general principle applied to phthalocyanines led to stable films at the water-air interface and could produce multilayers by the LB technique [82. 83]. 

Hydrophobic regions are indicated by the distribution of hydrocarbon chains and aromatic rings. Carboxylic acid and phenolic functional groups would confer polar characteristics and would account for the fact that SOM can retain a considerable... 

---