Olefins trans double bond

Olefin isomerization consists of three possible reactions (see Figure 14.4) cis-trans, double bond and skeletal. As noted by Damon, et al., [32, 33], cis-... 

In order to stop the reaction when the amount of monoole-finic product in the reaction mixture is highest, aliquots of the reaction mixture are removed at intervals and analyzed by infrared spectrometry or by gas chromatography. In the infrared spectrum the relative intensities of bands at 965 cm. (trans-CH=CH) and 702 cm. (m-CH=CH) are observed in successive aliquots. The reaction is stopped when the band at 965 cm.- attributable to the trans double bonds of the starting triene, has almost completely disappeared and the band at 702 cm.- (m-olefin) remains. 

The processes of olefin exchange, double bond migration and cis—trans isomerisation, observed to occur concomitant with hydrogenation, may be accounted for by considering that the formation of the half-hydrogenated state is reversible. For olefin exchange we can write... 

Use of benzene as a photosensitizer with cyclic olefins produces double bond shifts and addition of alcohols.253-254 The direction of addition suggests an ionic process. The reaction does not occur with acyclic, exocyclic, or sterically constrained olefins. A likely explanation253 is that olefin triplets formed by energy transfer decay in part to highly reactive trans-cycloa 1 kenes which are readily protonated. 

Since the olefinic CC double bond is trisubstituted, the relative configuration cannot be determined on the basis of the cis and trans couplings of vicinal alkene protons in the H NMR spec-trum. What is the relative configuration given the 13C NMR spectra 19 ... 

Platinum complexes incorporating an optically active amine have been employed for resolution of racemic mixtures of optically active olefins by reaction of the olefin with dichloro-platinum(II). The differing solubility of the diastereoisomers permits separation by fractional crystallization and the olefin can be recovered by reaction of the complex with aqueous alkali cyanide. Using either (-f)-l-phenyl-2-aminopropane (Dexedrine) or (-f)- or (—)-a-phenyl-ethylamine. Cope and co-workers have resolved the optical isomers of trans double bond coordinated and, with (—)-phenylethyl-amine)dichloroplatinum(II), a bridged complex with each double bond coordinated to a different platinum atom. 

In those cyclic olefins, having both cis and trans double bonds, complexing with silver ion occurs preferentially at the trans (372), undoubtedly as a result of the higher strain energy associated with the trans endooyclic double bond (416). The 2 1 and 3 1 stoichiometry of the... 

The stoichiometry of the crystalline complex obtained by reaction of cyclic oligoolefins with AuCl in absolute ether at room temperature (0°C for norbornadiene) depends upon the olefin. 1,5-Cyclooctadiene and both cis,cis,trans- and oif-infrared spectra of the trienes indicate the presence of both complexed and free double bonds, the cis,cis,trans-l,5,9-cyc odo-decatriene showing one free cis unsaturation. C is,cyclodeca-diene and dicyclopentadieneform, on the other hand, only 1 1 complexes. The former olefin is complexed only at the trans double bond, whereas the latter is complexed only at the double bond in the norbomene part of the molecule (225). 

The all-/ra/ij-sulphide 223 was found to be clearly diatropic having a mobile trans double bond as evidenced by the high field signals of and in the H-n.m.r. spectrum. The di-cw sulphide 224 also appeared to be diatropic, as indicated by the low-field position of the methyl proton resonance, but the chemical shifts of the olefinic protons suggest the conformational mobility of this molecule (i.e. 224a and b). The spectrum at - 75 °C showed the presence of about 45% of the symmetrical conformer 224a. The frozen spectrum confirms that 224 is diatropic, and undoubtedly also the biscyclohexene-annelated derivative 216 is considered to be diatropic but conformationally mobile. The all-rw/M-sulphone 225 was found to be atropic, whereas the di-cij sulphone 226 was clearly paratropic. This fact parallels the observations that the annelated sulphone 221 is atropic and the di-c/s isomer... 

Isomerization of cis- to txwas-olefins. Sgoutas and Kummerow1 reported in 1969 that m-unsaturated fatly acid esters are isomerized to trans-esters when heated at 65° in a sealed vial with thiols or diphenylphosphine in the presence of azobisisobutyronitrile. The equilibrium mixture contains 75-80% trans double bonds. There is no migration of the double bonds. Presumably addition of thiyl or phosphinyl radicals to the double bond is involved. 

The preferences of the various pathways are dependent on the catalyst used, specifically the electronic and steric factors involved. The electronic contribution is based on the preference of the metallacycle to have the electron-donating alkyl groups at either the a or the carbon of ftie metallacycle [23]. The steric factors involved in the approach of the olefin to the metal carbene also determine the re-giochemistry of the metallacyclobutane formed. These factors include both steric repulsion of the olefin and carbene substituents from each other and from the ancillary ligands of the metal complex. Paths (b), (c), and (e) in Scheme 6.10 are important to productive ADMET. The relative rates of pathways (c) and (e) will determine the kinetic amount of cis and trans double bonds in the polymer chain. Flowever, in some cases a more thermodynamic ratio of cis to trans olefin isomers is attained after long reaction times, presumably by a trans-metathesis olefin equilibration mechanism [31] (Scheme 6.11). 

Polymers of containing both cis and trans double bonds can be made with other catalysts but the cis double bonds are never found within HH dyads. An example of the n.m.r. spectrum of the olefinic carbons in such a polymer (Cj. = 0.48) is shown in Figure 2. The trans HH signal is equal to the sum of the trans TT and cis TT signals and there is no resonance that can be ascribed to cis HH,... 

Normally 1,1-disubstituted double bonds react faster with protons than do 1,1,2-trisubstituted ones because the former are more polarisable, a feature which protons prefer. However, in the case of caryophyllene, the endocyclic trans double bond is so strained that the normal reactivity pattern is reversed and it is this bond which is protonated first. In Figure 7.35, protonation of the endocyclic double bond is rapidly followed by addition of the electrons of the exocyclic bond to give the tricyclic carbocation (7.164). As would be expected, in both instances, the electrophile is added to the less substituted end of the olefin. The carbocation can be trapped by water to give the alcohol (7.165) which is known both as caryophyllene alcohol and caryolanol. Alternatively, a 1,2-carbon shift can occur to reduce strain... 

The cis content in all these polymers can be readily determined from either their or H NMR spectra. The H NMR spectrum of polynorbomene gives well-resolved olefinic proton signals (multiplets) at 5.35 ppm (i) and 5.21 ppm (c), also a-proton signals (fine structure unresolved) at 2.8 ppm (c) and 2.45 ppm (r) (Larroche 1982). The C NMR spectra give, in addition, information on the proportions of double-bond dyads and triads, and hence on the distribution of cis and trans double bonds. There are two main questions to be answered (i) what... 

Panek s group ° employed the Schlosser-Wittig olefination reaction of an in situ-generated tris-oxazole phosphonium salt to incorporate the trans double bond of an advanced intermediate leading to ulapualide A (Scheme 1.397). Model studies that precedent this work were described in Scheme 1.298. Thus reaction of 1560 with 1561 in the presence of excess triethylphosphine and one equivalent of LDA generated 1562 in excellent yield as a single double-bond isomer. This result was noteworthy in that it demonstrated the viability of this type of bond construction in the presence of a potentially labile p-alkoxy substituent. 

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