Shortening, trans isomers

Unsaturated fatty acids usually contain a cis double bond at position 9 or 12—e.g., linoleic acid (18 2 9,12). As with saturated fatty acids, degradation in this case occurs via p-oxida-tion until the C-9-ds double bond is reached. Since enoyl-CoA hydratase only accepts substrates with trans double bonds, the corresponding enoyl-CoA is converted by an iso-merase from the ds-A, cis- A isomer into the trans-A, cis-A isomer [1]. Degradation by p-oxidation can now continue until a shortened trans-A, ds-A derivative occurs in the next cycle. This cannot be isomerized in the same way as before, and instead is reduced in an NADPH-dependent way to the trans-A compound [2]. After rearrangement by enoyl-CoA isomerase [1 ], degradation can finally be completed via normal p-oxidation. 

While in the ferrioxamine biomimetics the aim was to reduce the conformational freedom by shortening the length of the spacers to prevent formation of mer (trans) isomers and favor instead the exclusive formation of the fac (cis) isomers, in preparing coprogen analogs the mer isomers are pursued. 

In methylene chloride or DMSO solution in the presence of catalytic amounts of protonic acids (81CC828,81ZOK2064) or under UV irradiation (81ZOK2064) cis isomers lb transform into a 1 1 mixture of cis and trans isomers, indicating the expected energy equivalence of la and lb. Both of these are characterized by an equal number of shortened intramolecular Te. . . H contacts, which were revealed by an X-ray study of trans isomer la (Ar=C6H5)(81TL1495) (Fig. 1). 

Fatty acid triesters of glycerol containing the unnatural trans isomers of fatty acids. Trans fats are often formed as by-products in the partial hydrogenation of vegetable oils to produce margarine and vegetable shortening, (p. 1205)... 

A fluorine substituent shortens the adjacent C—C bonds and lengthens the opposite bond in the cyclopropane ring. The lengthening of the C—C bond opposite to a CF2 group is remarkable (cf 98 and 104 in Table 9), but the mean C—C distance is smaller even in these molecules than in cyclopropane (1). In the other fluoro derivatives, all C—C bonds are shorter than in 1. The C—C bonds appear to be longer, the C—F bonds shorter in a cis isomer than in the trans isomer , and the same applies to C—C and C—F bonds in cis compared to trans CHF—CHF moieties within the same molecule. Ab initio calculations with a 4-2IG split valence basis set reflect the above trends quite well, except for the distinction of effects in the cis and trans forms ". The additivity of substituent effects, which... 

Nutrition. Fats and oils are recognized as important nutrients for both humans and animals because they provide a concentrated source of energy, contain essential fatty acids, and serve as carriers for fat-soluble vitamins. Research studies have also indicated a relationship between saturated fats, cholesterol, and trans-isomers and the incidence of coronary heart disease. In many cases, shortening functionality can be maintained with formulations limiting cholesterol, the identified saturated fatty acids, and tran -isomers. Shortening formulation can also aid in reductions of fat consumption by development of more effective products to reduce the levels required to produce the desired functionality and finished product quality. 

Stereoisomers include cis and trans isomers, chiral isomers, compounds with different conformations of chelate rings, and other isomers that differ only in the geometry of attachment to the metal ion. As mentioned at the beginning of this chapter, study of stereoisomers provided much of the experimental evidence used by Werner to develop and defend his coordination theory. Similar study of new compounds is useful in establishing structures and reactions, even though development of experimental methods such as automated X-ray diffraction can shorten the process considerably. 

Some unsaturated hydrocarbons are converted to saturated hydrocarbons in the manufacture of high-octane gasoline and aviation fuels. Unsaturated vegetable oils can also be converted to solid cooking fats (shortening) by hydrogenation of most of the carbon-carbon double bonds present (Figure 27-21). Most of the double bonds that remain are the trans- isomer. 

Precht, D. and J. Molkentin. Recent Trends in the Fatty Acid Composition of German Sunflower Margarines, Shortenings and Cooking Fats with Emphasis on Individual C16 l, C18 l, C18 2 C18 3 and 20 1 Trans Isomers. Nahrung44-. 222-228 (2000). 

Hull and Bartlett have also identified and quantified the products from the photosensitized addition of cis- and trans-1-chloropropene to cyclopentadiene. The relative amounts of cis- and trans-isomers in the products were about the same irrespective of the olefin used in the addition, but the product mixtures from each differed with respect to individual isomers. The regioselectivities and reactivities of the olefins are consistent with the formation of a triplet biradical whose lifetime with respect to spin inversion and closure is appreciably shortened by the presence of the halogen within the biradical. 

Precht, D and Molkentin, J (2000) Recent trends in the fatty acid composition of German sunflower margarines, shortenings and cooking fats with emphasis on individual Cl6 1, C18 l, C18 2, C18 3 and C20 l trans isomers. Nahrung, 44, 222-228. 

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