Shift of double bond

Light-activated shift of double bonds in organic compounds can promote the reaction of oxygen with a molecule. Once oxygen has bonded to a fuel component, oxidized organic compounds such as alcohols, aldehydes, esters, ethers, and acids can form. These compounds can then continue to react with other fuel components to form color bodies, gums, and insoluble deposits. 

Zelinskil and Levina studied the shift of double bonds when olefins were passed over oxide catalysts (446). Levina also established that in the presence of chromic oxide on alumina at 250° the triple bond in a 1-alkyne is shifted, giving a product one half of which consists of the corresponding 2-alkene and one-half of a 1,3-diene (206). She also reported migration of double bonds from side chains into the ring of naphthenes carrying unsaturated side chains. 

The process entails shifting of double bonds along the polyene chain, with the formation of a "retro-retinal" structure. Peters et al. (301) interpreted their observations by identifying PBAT with an excited state of rhodopsin, where single proton transfer toward the Schiff base nitrogen leads to the formation of bathorhodopsin. This approach has been supported by the theoretical interpretation of the spectrum of rhodopsin in terms of a nonprotonated Schiff base (214-216). A mechanism involving deprotonation of the Schiff base has also been suggested (310). All these models do not require cis-trans isomerization as a primary event in the chromo-phore. 

Ill the presence of hydrogenation catalysts, unsaturated compounds undergo not only hydrogenation but also isomerization—shift of double bonds, or stereochemical transformations—which also affects physical and chemical properties.)... 

There is also a correlation of C NMR chemical shifts of the a- and p-carbons of di- and tri-sub-stituted a,p-unsaturated acids, represented by the empirical relation in equations (2a) and (2b), which relies on the additive shielding increments Another method used for the determination of double bond configuration makes use of effects induced by benzene or other aromatic solvents on the chemical shifts of double bond substituents preferential shielding of protons or alkyl groups trans to the polar groups is usually observed. An example of the use of this method is the determination of the stereochemistry of the double bond in (Z)- and ( -geranic acids (6 and 7 Scheme 6). ... 

In general, then, if the attempt is made to prepare a molecule containing two unpaired electrons, and that molecule is such that these two electrons may interact with each other through the molecule merely by the shifting of double bonds, that interaction will take... 

Conjugated dienes and trienes measure the shift of double bonds. The shift is measured by the absorbences at 232 and 268 nm. Similar to the peroxide value, the absorbance at 232 nm measures the level of reactive intermediates. values, which are very low in unheated oils, may become as high as 15 within a few days of commercial frying. values at 268 nm follow changes in the iodine value, viscosity, PEFA, and polymer content. 

The substituted adenine i.e., 2-chloro-9-(2-hydroxyethoxy-methyl) adenine is treated with pure sodium nitrite in glacial acetic acid and ammonia gas is passed through the reaction mixture for a stipulated period when the amino function gets rearranged from C-6 to C-2 together with a carbonyl moiety at C-6. Besides, there is a shift of double bond between positions from 2-3 and 5-6 to 2-3 and 4-5. 

Spin trapping with PMNB was applied to the radicals derived from initiator decomposition (formula 3) and their subsequent reactions with the model compounds (formula 5). Both initiator radicals could be trapped and identified. When model compounds were present during UV-irradiation, new radicals were identified from the ESR spectra. For dihydrocyclopentadiene (DHCPD) only one trapped radical was found and for ethylidene norbornane (ENB) two radicals. By comparison with computer simulated ESR spectra, it is concluded that the radicals of these model compounds are all allyl radicals (formula 8 and 9) formed by hydrogen abstraction from the models. Radical (8 a) has two stereoisomers but they have closely the same ESR spectra when trapped and cannot be separated. Radical (8 b) has two resonance structures (shift of double bond in the ethylidene group) but only one radical (8 b) is trapped, probably due to steric hinderance for trapping the methin radical. The DHCPD radical (formula 9) has two steric forms because the two allylic hydrogens are not identical. Once they are formed, the spin trap can only approach from one side and only one of the steric forms is trapped as shown in the ESR spectrum. 

Saturated fatty acids with an even number of C-atoms are degraded totally to acetyl GoA by repetition of these reactions. Unsaturated fatty acids have to be converted during the course of degradation to compounds which can be attacked by the enzymes of / -degradation, e.g., by isomerization, shift of double bonds, hydration etc. (Fig. 54). 

The basic skeleton of isoprenoids may be modified by the introduction of a wide variety of chemical groups, by isomerization, shift of double bonds, methyl groups, etc. Hence a bewildering number of chemical structures arises. In addition compounds derived from other biogenic pathways may contain isoprene residues. For instance the K vitamins (D 8.1), ubiquinones (D 8.3), chlorophylls (D 10.1), plastoquinones, and tocopherylquinones (D 22.4) have isoprenoid side chains with up to ten isoprene units. Polyketides (D 3.3), alkaloids (D 8.4.2), and coumarins (D 22.2.2) may be substituted by dimethylallyl groups. The terpene residues are attached to nucleophilic sites, such as active methylene groups and phenolic oxygen atoms. 

The biosynthesis of cyclic sesquiterpenes probably includes the formation of enzyme-bound intermediates (Figs. 107 and 108). It is accompanied by the shift of double bonds, hydride ions, etc. The diversity of chemical structures of sesquiterpenes is greater than that of mono-, di-, and triterpenes due to the many different types of cyclizations occuring in this group of secondary products. 

Enzyme systems from outside genus Claviceps transform agroclavine mostly to 8-hydroxyderivatives (Figure 1). These conversions are mediated mainly by peroxidases. The 8-oxidation of 8, 9-ergolenes is accompanied by the shift of double bond to 9, 10-position. Intermediates of this reaction are in some cases 10-hydroxy- or 8, 9-epoxy-derivatives. 

The shifts for carbons of double bonds generally range from 80 to 160 ppm and they can again be estimated from empirical rules based on substituent effects. Thus the shifts of double bond carbons can... 

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