The Determination of cis-trans isomer is important in some cases. The chemical method is a conventional technique to determine the cis-trans isomers. It is very much important in chemistry because the same compound which has cis as well as a trans isomer, can act differently; though they have the same chemical structure. So not done any delay let’s discuss the matter.
The cis-trans isomer is the geometrical isomer. The isomer is arisen due to the inhibition of the rotation through the sigma bond of molecules. The cis-trans isomers of the molecules take place because of the rigidity of the bonds of a molecule. The rigidity of the molecules happens because of the presence of double bonds or cyclic structure of the compound. That means the rotation must be prohibited by any means.
Determination of configuration of cis-trans Isomers
The configuration of cis-trans Isomers can be determined by chemical as well as physical methods. Determination of the configuration of cis-trans isomers is useful for the study of the physical and chemical properties of the compound. As we know the chemical and physical methods are useful for the determination of the detection of the cis-trans isomer, we will discuss briefly the chemical methods. Now,
- Chemical methods: rest on a firm basis, now largely of historical interest.
- Physical methods: simpler and easier to employ (mainly spectroscopic).
In this post, we will discuss mainly the chemical method of the Determination of the configuration of cis-trans Isomers.
There are three methods under the chemical method. With the help of those methods, we can easily find the configuration of cis-trans Isomers. The methods are-
- Absolute method
- Correlative not affecting the configuration of the double bond method, and
- Mechanistic method.
Now let’s know the method briefly-
this process is based on the following points-
- Functional groups in cis isomers located cis to each other can be converted into cyclic lactones, anhydrides, amides but not the trans isomer
- cis isomers can be synthesized from the small rings compounds but the trans isomers do not do the same.
A third way of assigning E or Z configuration to an alkene is by a directed ( means that the stereo chemical outcome of the reaction chosen can be confidently predicted) stereospecific ( one stereo isomer reacts preferentially over another stereoisomer) .
a ) addition to alkynes ( acetylenes): syn addition of organocopper reagent followed by alkylation (preparation of trisubstituted alkene of defined configuration.)
b) synthesis from saturated compounds of known configuration. If we can synthesize the same compound which is determined the configuration from a known compound then the configuration of the known compounds and the other compound is the same.
c) Other methods most suitable of which is Wittig reaction: Substantial stereoselectivity & thereby prediction of the configuration of the product may be obtained in the following Wittig reaction-
From the above discussion, we can learn about the Determination of the configuration of cis-trans Isomers in the chemical method.