Chemical concept

Chemical concept: Isomers – Enantiomers: R and S Nomenclature 

Isomer of a molecule is a molecule that has similar chemical formula but with different arrangements of atoms. The broad topic of isomer is split into 2 sub topics namely constitutional isomer and stereo-isomers. Stereo-isomers is further split to diastereomer and enantiomers. 

Constitutional isomer is when the atoms are arranged in different order yet having same molecular formula. Diastereomer refers to cis/trans isomer. while molecules that are mirror images of each other are known as enantiomers.

 

Zooming in to Enantiomers~

Enantiomers consist of one or more chiral center. Chiral center is when a carbon atom has four different substituents around it. The molecules are not superimposable to one another just like our hands.

*Not superimposable is when two molecules were placed on top of one another and yet unable to get the same molecules no matter how you rotate it*

Priority was assigned to each group attached to the chiral center based on the Cahn-Ingold0-Prelog priority rules. After which, classify the molecules as R-stereoisomer or S-stereoisomer based on the direction of priority order.

If is clockwise, then it is R-stereoisomer; If is anti-clockwise then it is S-stereoisomer.

The R and S classification system to distinguish enantiomers. R and S isomer have different biological activity and can be interconverted via enzymatic activity in our body.

Importance of isomerism in pharma field: both enantiomers have different chemical properties thus bring different biological effect in our body since they are able to interconvert in our body. Hence to avoid cases like thalidomide (as mentioned in the introduction), pharmaceutical companies have been doing tests (mentioned in the how drugs are made)  to make sure that the drugs are safe.

References:

  1. ChemEd DL. (n.d.). Definitions: Isomers. Retrieved March 31, 2017, from Chemddl.org/resources : http://www.chemeddl.org/resources/stereochem/definitions1.htm
  2. Dr. Ian Hunt, D. o. (n.d.). Basic IUPAC Organic Nomenclature . Retrieved March 31, 2017, from Chem.ucalgary : http://www.chem.ucalgary.ca/courses/350/orgnom/stereo/stereo-03.html
  3. “Allotropes vs Isomers.” Diffen.com. Diffen LLC, n.d. Web. 6 Apr 2017.< http://www.diffen.com/difference/Allotropes_vs_Isomers >