Double bond number, conjugated dienes

Double bond number, conjugated dienes, 671 Double bonds carbon-carbon... 

RP-HPLC with nonaqueous solvents and UVD at 246 nm was developed for the determination of low level POVs of vegetable oils. These measurements are specific for conjugated diene peroxides derived from vegetable oils with relatively high linoleic acid content. These measurements may be supplemented by nonspecific UVD at 210 nm and ELSD for detection of all eluted species. The elution sequence of the triglycerides in a nonaqueous RP-HPLC is linearly dependent on the partition number of each species, Vp, which is defined as = Nq — 2Ni, where Nq is the carbon number and is the double bond number. In the case of hydroperoxides = Nq — 2Nd — Vhpo, where Vhpo is the number of hydroperoxyl groups in the molecule (usually 1 for incipient POV). For... 

Note, too, the mild conditions used for the formation of the diisopropyl acetal 552 from aldehyde 55,1 again without p-elimination. Another example comes from a synthesis of Arachidonic Add in which a key step was the mild hydrolysis of a diisopropyl acetal under conditions that do not provoke rearrangement of the p,y-double bond into conjugation with the aldehyde function.118 The method has been applied to the synthesis of a number of natural (Z,Z)-skipped 1,4-dienes.119... 

Dienes are very important monomers. The molecule of any diene may carry various substituents. In spite of the great number of possible variants, fewer are employed in production and science than in the case of vinyl monomers. The mutual position of double bonds, cumulative, conjugated or isolated, is of great importance. 

Addition of deuterium to ergosterol acetate was shown to form the 5a,6a-dideuterio reduction product under mild conditions (Equation 15.4). This result illustrates a number of features of the reactivity of Wilkinson s catalyst. First, the conjugated diene is reduced in preference to the C21-C22 double bond. Second, the diene is reduced from the less-crowded a-face of the steroid. Neither the remaining trisubstituted double bond nor the trans disubstituted A double bond are affected. Finally, no isotopic exchange takes place during this reaction. This selectivity has been used to specifically label prostaglandins with tritium (Equation 15.5). The sensitive 3-keto alcohol is unperturbed. 

Cyclopentadiene contains conjugated double bonds and an active methylene group and can thus undergo a Diels-Alder diene addition reaction with almost any unsaturated compound, eg, olefins, acetylene, maleic anhydride, etc. The number of its derivatives is extensive only the reactions and derivatives considered most important are discussed. 

Double-bond migration often passes unnoticed, for unless tracers are employed, there may be no direct evidence remaining that migration has occurred. Nonetheless, the fact that it does occur can have a number of important consequences. Selective removal of cis homoconjugated dienes and trienes in natural oils, used to make edible hydrogenated fats, depends mainly on prior isomerization of multiple unsaturation into conjugation under hydrogenation conditions (J9). 

Even simple dienes and polyenes are difficult to classify in comparison with alkenes. Whereas bromination, oxidation and reaction with tetranitromethane (TNM) can identify the number of double bonds and their location in the molecular structure, conjugated double bonds produce very complex mixtures. Furthermore, many of the tests based on 7r-complexation can also apply for aromatic moieties. An example is the TNM 7r-complex which is yellow with benzene and orange with naphthalene and the tests are therefore non-specific. 

Most methods used for analysis of alkenes, such as bromination and hydrogenation, can be employed to determine the number of double bonds in polyenes. These methods were also employed to classify various petroleums ( bromine number ). However, these classical methods are employed less in analysis of conjugated dienes and polyenes mostly because the products produce a less informative mixture than in the alkene case. 

Study of the photochemistry of myrcene, 23, a triene containing both a conjugated diene system and a remote, unconjugated double bond, has been exceptionally informative. Direct excitation produces a cyclobutene derivative 24, /S-pinene, and a host of minor products287 including 25. In contrast, indirect excitation using a number of sensitizers gives only a derivative of bicyclo[2.1.1]hexane, 25.288... 

The conjugated dienes can polymerize in four modes cis 1,4-, trans 1,4-, 1,2- and 3,4-, the latter pair being equivalent in the absence of appropriate substitution. Early workers relied entirely upon IR spectroscopy to analyze the concatenation in their polymers. There are a number of problems associated with the technique correct assignment of peaks, the additivity and the inherent insensitivity arising from the smallness of the extinction coefficients of double bonds bearing more than one substituent (such as arises from 1,4-enchainment). In consequence, the reliability of much of the early work is uncertain the advant of NMR spectrometers has,... 

Allenic hydrocarbons, including cyclic ones, underwent chlorine addition under radical conditions only one double bond reacted [12], A number of conjugated dienes added chlorine in their reaction with (dichloroiodo)benzene under radical conditions. Both 1,2- and 1,4-addition occurred their ratios varied, depending on the substitution of the non-cyclic substrate and the size of the cyclic ones trans products were normally favoured [13]. 1,6-Dienes were cyclized to 1,2-bis chloromethyl cyclopentanes [14] ... 

The extra stabilization provided by delocalization, compared with a localized stmcture. For dienes and polyenes, the resonance energy is the extra stability of the conjugated system compared with the energy of a compound with an equivalent number of isolated double bonds, (p. 669)... 

---