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 firm basis, now largely of historical interest.
- Physical methods: simpler and easier to employ ( mainly spectroscopic).
In this post we will discuss about 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 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 isomaers
- 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 organo copper reagent followed by alkylation ( prepn of trisubstituted alkene of defined configuration.
b) synthesis from saturated compounds of knows configuration. If we can synthesize the same compound which to be determined the configuration from a known compound then the configuration of the known compounds and the other compound are same.
c) Other methods most suitable of which is Wittig reaction: Substantial stereoselectivity & thereby prediction of the confign 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 chemical method.