Cis-trans isomers of alkenes

It should be clear to you that there will be no cis-trans isomers of alkenes in which one end of the double bond carries identical groups. Thus we do not expect there to be cis-trans isomers of 1-butene or 2-methylpropene, and... 

ACD/H-NMR from Advanced Chemistry Development (ACD) Labs calculates H-NMR spectra under any basic frequency. The system uses 3D molecular structure minimization and Karplus relationships to predict proton-proton coupling constants. The software recognizes spectral differences among diastereotopic protons, cis-trans isomers of alkenes, syn-anti isomers of amides, oximes, hydrazones, and nitrosa-mines. The base data set includes more than 1,000,000 experimental chemical shifts and 250,000 experimental coupling constants. To quantify intramolecular interactions in new organic structures and to predict their chemical shifts, ACD/HNMR uses an algorithm based on intramolecular interaction parameters to quantify intramolecular interactions in new organic structures and to predict their chemical shifts. 

Cis-trans isomers of alkenes (Section 1.13B) have different physical properties. They have different melting points and boiling points, and often cis—trans isomers differ markedly in the magnitude of their dipole moments. Table 2.2 summarizes some of the physical... 

Draw the condensed structural formulas and give the names for the cis-trans isomers of alkenes. 

Geometric or cis-trans isomers of alkenes occur when the carbon atoms in the double bond are connected to different atoms or groups. 

Infrared and Raman spectra. The infrared spectra of cis-trans isomers of unsymmetrical alkenes of the type R-CH=CH-R show characteristic differences... 

An important problem in many syntheses is to produce the desired isomer of a cis-trans pair of alkenes. The problem would not arise if it were possible to isomerize the undesired isomer to the desired isomer. In many cases such isomerizations can be carried out photochemically. A typical example is afforded by cis- and /raw.v-1,2-diphenylethene (stilbene) ... 

In addition to the alkene isomers that exist because of double-bond position, alkene isomers can also exist because of double-bond geometry. For instance, there are two geometrical, or cis-trans isomers, of 2-butene, which differ in their geometry about the double bond. The cis isomer has its two -CH3 groups on the same side of the double bond, and the trans isomer has its two -CH3 groups on opposite sides. Like other kinds of isomers we ve discussed, the individual cis and trans isomers of an alkene are different substances with different physical properties and different (although often similar) chemical behavior. cfs-2-Butene boils at 4°C, for example, but trans-2-butene boils at 0.9°C. 

Carbon-carbon double bonds cannot rotate, and many alkenes show geometric (cis-trans) isomerism (Sections 2-7B and 2-8B). The following are the cis-trans isomers of some simple alkenes ... 

Compounds with different arrangements of groups on either side of a bond with restricted rotation, such as a double bond or a single bond in a ring for example cis-trans isomers of certain alkenes. 

Although the cis-trans interconversion of alkene isomers does not occur spontaneously, it can be made to happen by treating the alkene with a strong acid catalyst. If we interconvert cis-2-butene with tmn.s-2-butene and allow them to reach equilibrium, we find that they aren t of equal stability. The titans isomer is more favored than the cis isomer by a ratio of 76 to 24 ... 

For distinguishing cis/trans isomers of conjugated polyenes or of alkenes, Randic et and then Pogliani started from the observation that in an s-cis butadi-... 

The reaction hexenes —> hexadienes was demonstrated without using radiotracers both on oxide and metal catalysts, Nil 1 and Ptj l Mixtures containing [ " CJ-hexene contributed to the clarification of the further reaction pathway. These studies showed that neither the hexene cyclohexane nor the hexene —> cyclohexene ring closure pathway took place.Table 2 indicates that radioactivity appeared in both the hexatriene and 1,3-cyclohexadiene fractions when their inactive form was admixed to radioactive hexene. The aromatisation of both inactive components was much more rapid than that of hexene, therefore their specific radioactivities showed very low absolute values, however, these were still higher than that of benzene produced mainly from these non-radioactive precursors. The true precursor of ring closure should have been cis-cis-1,3,5-hexatriene. Its ring closure takes place without any catalyst from 513 The stepwise dehydrogenation of open-chain hydrocarbons produces cis- and trans-isomers of alkenes and alkadienes. Any c s-c s-triene... 

Cis and trans isomers of alkenes do not have the same stability. 

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