Determination of configuration of cis-trans Isomers
The configuration of cis-trans Isomers can be determined by chemical and physical method. Determination of configuration of cis-trans Isomers is useful for the study of Stereochemistry.
- 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 Determination of 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.
- Absolute method
- Correlative not affecting the configuration of the double bond method and
- Mechanistic method.
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 are 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 configuration of cis-trans Isomers in the chemical method.