Trans/cis configurations

Measurement of Unsaturation. The presence of double bonds in a fatty acid side chain can be detected chemically or through use of instmmentation. Iodine value (IV) (74) is a measure of extent of the reaction of iodine with double bonds the higher the IV, the more unsaturated the oil. IV may also be calculated from fatty acid composition. The cis—trans configuration of double bonds may be deterrnined by infrared (59) or nmr spectroscopy. Naturally occurring oils have methylene-intermpted double bonds that do not absorb in the uv however, conjugated dienes maybe deterrnined in an appropriate solvent at 233 nm. 

Thermal decomposition of [N(PPh3)2]" -[S4N5] in MeCN yields sequentially the corresponding salts of S3N3 and S4N (50% yield). An X-ray crystallographic analysis of the dark-blue air-stable product [N(PPh3)2] [S4N] revealed the presence of the unique acyclic anion [SSNSS] whose structure is in Fig. 15.42c. The anion is planar with cis-trans configuration. 

Hydrogenolysis of the acetylene-cumulenes 19 can be achieved by means of a partially poisoned palladium catalyst to yield the regular [22]porphyrin(2.2,2.2) 20 with cisjrans.cis,-trans configuration of the two-carbon bridges. 

The thermodynamically favorable bis(r 3),A-cis/trans configuration 7b of the [Nin(dodecatrienediyl)] complex also represents the catalytically active species for reductive elimination. The new C-C a-bond is preferably established between the terminal unsubstituted carbons on two r 3-allylic groups (Fig. 9) giving rise to the formal 16e [Ni°(CDT)] product 8b, where CDT is coordinated to nickel by its three olefinic double bonds. 

The same allylic species can be formed from the related 1,3-diene and indeed cw,ci5-l,3-cyclodecadiene yields at least 38% tmns-cyclodecene although the saturation of one double bond which did not involve its neighbor should obviously yield the more stable cis isomer. The result implies that the allylic intermediate, which would be formed initially in the cis,cis conformation, has time to rearrange on the siurface to its more stable cis,trans configuration before it reacts further with hydrogen. The possibility that the ct ,cts-l,3-cyclodecadiene isomerizes first to the less stable cis,trans-diene was discounted. The rearrangement of the allylic intermediate could be accomplished via a o-bonded complex, as indicated on page 142 of Section III,C. 

From the analysis of a NOESY spectmm, it is possible to determine the three dimensional stmeture of a molecule or parts of a molecule. The NOESY spectmm is particularly useful for establishing the stereochemistry (e.g. the cis/trans configuration of a double bond or a ring junction) of a molecule where more than one possible stereoisomer exists. 

Triacylglycerols are quantitatively the most important class of dietary fats. Their biologic properties are determined by the chemical nature of the constituent fatty acids, in particular, the presence or absence of double bonds, the number and location of the double bonds, and the cis-trans configuration of the unsaturated fatty acids. 

Which of the following compounds could exist as cis-trans configurational isomers ... 

Finally monodentate N-coordination has also been observed for metal atoms in a zerovalent oxidation state. Examples are M(CO)5(RNSNR) (M = Cr, Mo, W R = Me, Et, Pr ) with the metal atom bonded to the N atom at the cis side of the sulfurdiimine ligand in the cis, trans configuration.1 18... 

A number of geometric isomers of retinol exist because of the possible cis-trans configurations around the double bonds in the side chain. Fish liver oils contain mixtures of the stereoisomers synthetic retinol is the all-trans isomer. Interconversion between isomers readily takes place in the body. In the visual cycle, the reaction between retinal (vitamin A aldehyde) and opsin to form rhodopsin only occurs with the 11 -cis isomer. 

As described above, the stereochemistries of the mulberry Diels-Alder type adducts could be divided into the following two groups one is an all-trans in relative configuration and the other is a cis-trans configuration. All-trans type adduct may correspond to an exo-addition product in the Diels-Alder reaction of a chalcone and a dehydroprenylphenol, whereas a cis-trans type adduct corresponds to an endo-addition product in the reaction. 

Double bond cis-trans configuration The saturated carbon chain is... 

Synthetic pyrethroids are geometric isomers with cis, trans configurations. Commercially available preparations of cypermethrin contain a mixture of cis and trans isomers in various proportions, for example, 60 40 and 80 20. Cypermethrin (cis trans 60 40) 2.5% solution is equivalent to cypermethrin (ids trans 80 20) 1.25% solution for pour-on application to sheep. Permethrin, which is the active ingredient incorporated in ear tags for cattle and insecticidal collars for dogs and cats, contains a mixture of cis and trans isomers in the proportion 40 60. 

Cao, C. and Gao, S. (2005) Estimating enthalpies of formation of monoalkenes by the bonding orbitalconnecting matrix of molecular graphics and the steric effect of the cis/trans configuration. /. Mol. Struct. (Theochem), 718, 153-163. 

The product ratio in cis- and trans-2,3-epoxyhexanes observed in the epoxidation of cis- and trans-2-hexenes indicated the retention of the cis-trans configuration of the starting 2-hexenes. This observation demonstrates that the rotation around the C(2)-C(3) axis of the activated complex is strictly prohibited. Kinetic results and tests using propylene oxide and acetone as the starting substrate... 

Esterquats cause fewer problems for formulating ultras and concentrates [7], Carefully selecting structural details of the active such as the mono-, di-, and triester ratio, the presence of unsaturation on the alkyl groups and their cis-trans configuration, the pH value, and the particle size of the dispersion enables one to get stable, low-viscosity softeners containing 20 to 25% active [6], Another advantage of esterquats is that they do not stain fabrics [7],... 

Cyclization of glutaraldehyde (129) with nitromethane, which, when first attempted, seemed unprofitable,121 has been so elaborated122,123 as to provide, in 66% yield, frans,frans-2-nitro-l,3-cyclo-hexanediol (130, R = H), the thermodynamically most stable of the three possible isomers (one dl and two meso forms). The reaction has been extended to include nitroethane,124,125 nitroethanol,128 ethyl nitroacetate125 [which gave, preponderantly, 130 (R = Me, CH2OH, and C02Et)], 1-nitropropane,124 and phenylnitromethane (a-nitro-toluene)124 [which yielded products 131 (R = Et and Ph) that had the Dlu-cis-trans configuration]. 

Figure 1 shows the chemical structures ofcarotenoids which will be dealt with in this Section. The length and position of the conjugated system are different from one carotenoid to another. All the carotenoids, except for /3-apo-8 -carotenal, neurosporene, and spheroidene, contain a complete central structural motif which is terminated by the 6 and 6 carbon atoms. The dependence of the H-NMR, electronic absorption and resonance-Raman spectroscopic properties on the cis-trans configurations of the symmetric )3-carotene molecule can change when there is a lack of a complete central structural motif in a carotenoid or when the carotenoid is asymmetric. In the following three subsections, the spectroscopic properties of the carotenoid, )3-carotene, will be described first, and then those of other carotenoids will be mentioned. 

---