Determination of configuration of cis-trans Isomers

Determination of configuration of cis-trans Isomers chemical method

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.

Chemical methods:

There are three methods under the chemical method. With the help of those methods we can easily  find the configuration of cis-trans Isomers.

  1.  Absolute method
  2. Correlative not affecting configuration of the double bond method and
  3.  Mechanistic method.

Absolute method:

this process is based on the following points-

  1. Functional groups in cis isomers located cis to each other can be  converted into cyclic lactones , anhydrides, amides but not the trans isomaers
  2. 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) .

Three approaches

a ) addition to alkynes ( acetylenes): syn addition of organo copper reagent followed by alkylation ( prepn of trisubstituted alkene of defined configuration.

Determination of configuration of cis-trans Isomers

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-

Determination of configuration of cis-trans Isomers

From the above discussion we can learn about the Determination of configuration of cis-trans Isomers in chemical method.

Click here to read about the Determination of configuration of cis-trans Isomers in physical method

 

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