Isomers cis- and trans

R Stereoisomers (Section 4.2) are compounds whose atoms are connected in the same order but with a different geometry. Among the kinds of stereoisomers we ve seen are enantiomers, diastereomers, and cis-trans isomers (both in alkenes and in cycloalkanes). Actually, cis-trans isomers are just another kind of diastereomers because they are non-mirror-image stereoisomers. 

An interesting case of metal-assisted ring opening of (109) has been described by Wolczanski using the low-valent (silox)3Nb fragment that binds (109) in the //2(N,C) mode (Scheme 50). Derivative (113) undergoes C—N insertion by thermolysis in benzene at 70 °C only. The reaction gives 0.5 equiv. of (109) and 0.5 equiv. of (114) as a thermodynamic mixture of cis,cis-, trans,cis-, trans,trans- and cis,trans-isomers.255-257... 

See the Concepts and Skills Review for a review of structural diagrams and cis-trans isomers.)... 

Price, W.P., Jr., and Deming, S.N. (1979), Optimized Separation of Scopoletin and Umbelliferone and cis-trans Isomers of Ferulic and p-Coumaric Acids by Reverse-Phase High-Performance Liquid Chromatography, Anal. Chim. Acta, 108, 227-231. 

One of a number of molecular entities having the same atomic composition, but different line formulas and/or different stereochemical configurations. A distinction is usually made between structural isomers (molecular entities have the same atomic composition albeit different line formuls), stereoisomers (entities having different arrangements, usually noninterconvertable and nonsu-perimposable, in space), and cis-trans isomers (having different positions for substituents with respect to double bonds or sides of a ring structure). 

Molecules having the same type and number of isotopic atoms, albeit in different positions. CH2DCH (NH3+)C00- and CH3CD(NH3+)COQ- are examples of isotopomers. Certain stereoisomers and cis-trans isomers can also be regarded as isotopomers for example, (R)- and (5)-l-deuteroethanol, CH3CHDOH. 

We have chosen these schematic formulas, because the occurrence of syn/anti- and cis/trans-isomers gives rise to new problems, not discussed in detail in this publication (see Sect. 2.5). 

Insects make unsaturated as well as saturated hydrocarbons. The former as well as long-chain alcohols and their esters often form the volatile pheromones with which insects communicate. Thus, the female pink bollworm attracts a male with a sex pheromone consisting of a mixture of the cis,cis and cis,trans isomers of 7,11-hexadecadienyl acetate,13 and European corn borer males are attracted across the cornfields of Iowa by czs-ll-tetradecenyl acetate.14 Addition of a little of the trans isomer makes the latter sex attractant much more powerful. Since more than one species uses the same attractant, it is possible that the males can distinguish between different ratios of isomers or of mixtures of closely related substances. 

Exercise 30-3 Write structures for each of the opticai and cis-trans isomers that would be expected for the following isoprenoid compounds (refer to Table 30-1) ... 

The result of acid-catalyzed isomerisation of F-dienes depends on several factors structure of substrate, catalyst, and temperature. Action of SbF5 on terminal dienes under mild conditions causes a 1,3 fluorine shift occurring stereoselectively to give trans-, frans-, and cis-, trans- isomers of the corresponding internal dienes [160] ... 

Carbon-3 is a stereogenic center, and cis-trans isomers are possible at the double bond between C-4 and C-5. Therefore, four structures are possible (R or S at C-3, and E or Z at the double bond). 

Sebastiao, K.I., Almeida-Muradian, L.B., Romanelli, M.F., Koseki, P.M. and Villavicencio, A.L.C.H. (2002) Effect of gamma-irradiation on the levels of total and cis/trans isomers of beta-carotene in dehydrated parsley. Radiation Physics and Chemistry 63(3-6), 333-335. 

Describe the difference between structural isomers and cis-trans isomers. 

TABLE 11.8 The Amounts (and Cis/Trans Isomer Ratios) of Hydrogenolysis Product in Hydrogenation of Phenol and Methyl-Substituted Phenols over Iridium Catalyst3 ... 

Preparation of the two stereoisomers of perhydro-9b-boraphenalene was originally reported by Koster and Rotermund,6 and the present procedure (part A) is largely based on the procedure described by these authors. However, the original stereochemical assignment was incorrect and has been reversed.3 7 Furthermore, these authors did not use the thermal treatment described above, which appears essential to achieve isomerization of other constitutional isomers into perhydro-9b-boraphe-nalene.3 The original procedure for isomerization of the cis,trans isomer to the all cis isomer has been satisfactory. Contrary to the claim made by these authors,6 however, this isomerization does not lead quantitatively to the all cis isomer, but reaches an equilibrium, which consists of the all cis and cis,trans isomers in the ratio of 88 12 this ratio was also confirmed by reverse isomerization of the pure all cis isomer.5... 

The ultimate test of the theoretical predictions for the mechanism of cyclopropane stereomutation would be to use an optically active disubstituted cyclopropane in which the substituents were just isotopes of hydrogen. This is a challenging problem both from a synthetic standpoint and from an analytical one. The analytical difficulty is particularly acute because one has to analyze a small, volatile molecule for both optical purity and cis-trans isomer ratio, and both measurements have to rely solely on the difference between isotopes. There are no functional groups to be used as handles for an optically active NMR shift reagent and so determination of optical purity must come from direct measurement of rotations—with a probable maximum specific rotation of < 1 ° ... 

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