Numbering chains

Primary alcohols are produced either by the catalytic hydrogenation of methyl esters or by fatty acids derived from oils and fats, e.g., coconut oil (C12-C14) or tallow (Cl6-C18), or from synthetic sources. Alcohols manufactured from natural oils and fats and from the Ziegler-type processes produce even-numbered chain length primary alcohols. 

One final note on this topic involves an examination of diploid, triploid, and tetraploid plants for their leaf exudate hydrocarbons (Seigler et al., 1975). -Alkanes having odd numbered chains from to were recorded for almost all plants collected from several sites with much more limited distribution of hydrocarbons based on and C g. The hydrocarbon data do not assist in distinguishing groups within this species. 

Figure 3A shows the location of the double-bond relative to a functional group of the Type I monoenyl components. The unsaturation is observed at more than 40% of the possible positions. Double bonds at odd-numbered positions are more predominant than those at even-numbered positions, and an unsaturation at the 11-position occurs in all even-numbered chain skeletons. Compounds monounsaturated at the 4- or 6-positions have not been identified, although an odd-numbered chain component, E4-13 OAc,has been identified. Currently, it is a rare occurrence to find a component unsaturated at a new position, as double bonds at the 10-position in a C12 chain and the 3-position... 

Fig. 3A,B Double-bond positions of monoenyl components in Type I pheromones A counting from the functional group B counting from the terminal methyl group. See text for components with an odd numbered chain (C13, C15, and C17)...

We now take a closer look at the first stage of fatty acid oxidation, beginning with the simple case of a saturated fatty acyl chain with an even number of carbons, then turning to the slightly more complicated cases of unsaturated and odd-number chains. We also consider the regulation of fatty acid oxidation, the j8-oxidative processes as they occur in organelles other than mitochondria, and, finally, two less-general modes of fatty acid catabolism, a oxidation and [Pg.637]

Electrical conductivity studies on molten zinc carboxylates of even-numbered chain length from C6 to C18 are consistent with a small concentration of relatively mobile Zn2+ ions.779... 

The //-alkanes usually range in chain length from 21 to 31 or 33 carbons. Hydrocarbons with fewer than 20 carbons commonly occur as pheromones, defensive compounds and intermediates to pheromones and defensive compounds, but their volatility makes them unsuited to function as cuticular components, n-Alkanes have been found on almost every insect species analyzed, and can range from less than one percent of the total hydrocarbons, as in tsetse flies (Nelson and Carlson, 1986 Nelson et al., 1988) to almost all of the hydrocarbon fraction, as in the adult tenebrionid beetle, Eurychora sp. (Lockey, 1985). Depending upon the species, they can consist of essentially only one major component, such as n-pentacosane in the American cockroach, Periplaneta americana (Jackson, 1972) to a series of //-alkanes, such as the series from C23 to C33 in the housefly, Musca domes-tica (Nelson et al., 1981), with trace amounts to C37 (Mpuru et al., 2001). In all cases, the odd-numbered alkanes predominate, due to their formation from mostly two carbon units followed by a decarboxylation (Blomquist, Chapter 3, this book). Small amounts of even-numbered carbon chain //-alkanes often occur, and presumably arise from chain initiation with a propionyl-CoA rather than an acetyl-CoA. Occasionally, gas chromatographic analyses reveal similar amounts of even-numbered chain //-alkanes and odd-numbered chain components. This is a red flag that the samples must be checked for contamination. 

Although the fatty acid oxidation scheme works neatly for even-numbered chain lengths, it can t work completely for fatty acids that contain an odd number of carbons. P-oxidation of these compounds leads to propionyl-CoA and acetyl-CoA, rather than to two acetyl-CoA at the final step. The propionyl-CoA is not a substrate for the TCA cycle or other simple pathways. Propionyl-CoA undergoes a carboxylation reaction to form methylmalonyl-CoA. This reaction requires biotin as a cofactor, and is similar to an essential step in fatty acid biosynthesis. Methylmalonyl-CoA is then isomerized by an epimerase and then by methylmalonyl-CoA mutase—an enzyme that uses Vitamin Bi2 as a cofactor—to form succinyl-CoA, which is a TCA-cycle intermediate. 

Ziegler process to give linear even numbered chains... 

Metal-capped carbon chains can exist in several forms (A-D Chart 1), with uneven-numbered chains only as cumulenic or alkynyl-carbynic tautomers and to date, up to 20 carbon atoms have been used to join two... 

As found with other complexes discussed in this chapter, the prevalence of even-numbered carbon chains is a result of the use of Cn (n = even) synthons in their construction. A few examples of odd-numbered chains, particularly when end-capped by trinuclear clusters which form i3-methylidyne complexes, are known. The following discussion will consider complexes in order of increasing n. 

The best known mesoionic compounds have five-membered rings, and initially it was advocated by Baker, Ollis, Ramsden and other authors that only five-membered heterocycles which cannot be satisfactorily represented by any one covalent or ionic structure possessing a sextet of TT-electrons in association with the five atoms comprising the ring may be called "mesoionic". Here, following Katritzky, mesoionic means a mesomeric betaine. The first such compounds to be discovered were sydnones, followed by miinchnones and then by diazolones. In all these compounds the Z-type atom is part of a carbonyl group, and two Y-type atom chains separate two odd-numbered chains of X- and Z-atom chains. Only the main resonance structures are displayed in formulas (Figure 11). 

The effect of alkyl chain length on the structure of alkanethiols on Au(lll) was studied with CH3(CH2) iSH, where n = 2,4, 6, 8, 10, 11, 12, 14, 15, 16, and 18).i The results, in terms of HREEL spectra, are displayed in Figure 11. It is most interesting to note that the intensity of CH3 a-deformation mode at 1380 cm (171 meV) is profoundly dependent on the number of carbons in the alkyl chain It is present only when the number of carbon atoms is even (cf, the spectra labeled Cio, C12 and C le) it is absent when the number is odd (cf, the spectra labeled Cu andCis). This odd-even trend is caused by the fact that the orientation of the CH3 head is parallel to the surface for odd number of carbon atoms but perpendicular when the number is even (cf, the inset in Figure 11). As dictated by the dipole selection rules, only the oscillator that has a component perpendicular to the surface (as in the even number chain) would show HREELS activity. It can also be seen in the frequency region below 220 cm (27.3 meV) that more than one peak, separated by about 30 cm (3.7meV) are present this indicates the existence of multiple adsorption sites for the subject alkanethiols on Au(lll). 

Liquid polymers are useful as tackifiers for rubbers, 72) and acrylic coatings. The most interesting are hydroxytelechelic polybutadienes, especially liquid butadiene-acrylonitrile (85/15) copolymers (trademark CN-15, ARCO). This product, known since 1971 as a tackifier, has the following characteristics viscosity 493 poises at 30 °C, tv[n = 4400, hydroxyl number/chain = 2.5. The incorporation of 5% of CN-15 in ethylene-propylene rubber (EPT Nordel 1070) increases its tack considerably 173) close to that of natural rubber or butyl rubbers (Table 4.1). 

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