Chain saturated hydrocarbons

BDEs of C-H bonds 3.1 Chain saturated hydrocarbons Table 3.1 C-H BDEs in Chain Saturated Hydrocarbons  

The broken bonds (boldface=dissociated atom), AfH (R), kcal/mol (kj/mol) BDEs (boldface = recommended data reference in parentheses) Methods References 

Heptane CH3CH2(CH2)4CH3 Affi°(R) = 2(8.2) 98.0 410.0 Derived from AfH° in ref. 1986PED/NAY 

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Open-chain saturated hydrocarbons have the generic names alkanes and paraffins. In this article, terms such as hexanes, heptanes, and octanes are synonymous with C, C, and Cg alkanes, respectively, and do not refer to the straight chains of 6 carbons, 7 carbons, and 8 carbons, as defined in the lUPAC system. 

The chain and branched chain saturated hydrocarbons make up a family called the alkanes. Some saturated hydrocarbons with five carbon atoms are shown in Figure 18-11. The first example, containing no branches, is called normal-pentane or, briefly, n-pentane. The second example has a single branch at the end of the chain. Such a structural type is commonly identified by the prefix iso- . Hence this isomer is called /50-pentane. The third example in Figure 18-11 also contains five carbon atoms but it contains the distinctive feature of a cyclic carbon structure. Such a compound is identified by the prefix cyclo in its name—in the case shown, cyclopentane. 

Straight chain saturated hydrocarbon molecules from propane (C3H8) to octane (CgHis) were deposited from the vapor phase on platinum and silver(l 11) crystal surfaces in the temperature range 100—200 K. The ordered monolayer was produced first and then, with decreasing temperature a thick crystalline film was condensed and the surface structures of these organic crystals were also studied by LEED ... 

The quoted frequencies are for typical open-chain saturated hydrocarbon chains (R). Conjugation and cyclic structures will influence the absorption frequency. 

The stepwise electron reduction of C02, whether direct or indirect, catalyzed, or by direct transfer on an apparently inert conductive surface, has been the object of considerable attention since the first concise reports of formate anion production. Since then, the list of possible derivatives has grown from formates to carbon monoxide, methane, ethylene, and short-chain saturated hydrocarbons. As noted in Section 12.1, this area of research has been expanded in recent years [8, 80, 83], with information relating to increased yields, to the effect of electrode materials on selectivity, as well as further speculations on possible reaction mechanisms, having been obtained on a continuous basis. Yet, the key to these synthetic processes-an understanding of the relationship between the surface of the electrode and the synthetic behavior of the system-seems no closer to being identified. 

Fig. 3.79 Comparison of the mass spectra of straight chain and branched chain saturated hydrocarbons (a) decane (b) 2,6-dimethyloctane.

The first of the really successful coatings was a long-chain, saturated hydrocarbon with 18 carbons. These octadecyl- (ODS), RPi8, or Qg columns are still the most commonly used HPLC columns, primarily because of the versatility they have shown. Other packing materials have appeared with shorter or longer side-chains, and, with a variety of functional groups on the side-chains, greatly extended the possible separations that can be achieved with HPLC. 

Sandorfy was struck by the artificial character of this approximation. His first target was the series of normal chain saturated hydrocarbons. A preliminary note on his results was published in the Comptes Rendus de VAcademie des Sciences.6 After taking up his position in Montreal, he greatly extended this work by introducing three different approximations, which he called the C CH, and H approximations.7 The first was based only on the atomic orbitals of the carbons, the second used the hybrid sp3 orbitals of the carbons and the Is orbitals of the hydrogens, and the third included all the valence atomic orbitals of the carbons and the hydrogens. 

Compounds of carbon with hydrogen and other elements form the vast area of organic chemistry. Silanes and germanes are Si and Ge analogous of methane and short-chain saturated hydrocarbons, and can be prepared by various methods, such as reduction of halides with LiAlH4 ... 

Hydrocarbon molecules in which the carbon atoms are attached to each other only by means of single bonds are called saturated. Open-chain, saturated hydrocarbons form the group called alkanes, shown in Figure 1.3. Their names all end with the suffix ane. 

The origin of this electron-repelling tendency has not been clearly determined. Since much of the evidence for it has been obtained from displacement reactions (Chapter 4), it seems very reasonable that the sequence is not due principally to electron release but rather to the fact that the more bulky groups hinder the approach of an attacking ion. However, a similar order is observed with the ionization constants of the branched chain aliphatic acids which does indeed indicate the presence of a small permanent polarization (Table 4). Since branched chain saturated hydrocarbons have no dipole moment, the electron-repelling tendency of an alkyl group in a saturated molecule must be small unless it is attached to an electron-attracting atom. 

Figure 27-6 A plot of normal boiling point versus the number of carbon atoms in straight-chain, saturated hydrocarbons.

A paraffin antifoulant may be employed, if desired, although it is not preferred, and any long-chain, saturated, hydrocarbon wax or oil may be used. 

When the nonaqueous phase is a straight-chain saturated hydrocarbon, the value of Tm is close to that at the aqueous solution-air interface, with possibly a slight increase in the effectiveness of adsorption as the length of the alkane is increased. When the nonaqueous phase is a short-chain unsaturated or aromatic hydrocarbon, however, there is a significant decrease in the effectiveness of adsorption at the aqueous solution-hydrocarbon interface (Rehfeld, 1967 Murphy, 1988). 

It was found that distribution equilibria are not very sensitive to the composition of the hydrocarbon diluent, provided that it consists mostly of saturated (paraffinic or naphthenic) hydrocarbons containing about 12 carbon atoms per molecule. However, Purex plants now usually specify a synthetic, straight-chain, saturated hydrocarbon made by polymerizing and hydrogenating lower olefins, which contains an average of 12 carbon atoms and is mostly n-dodecane. 

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