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 A D-isomer is defined as a stereoisomer which rotates light that is polarized in a clockwise direction[1]. This differs from an L-isomer which rotates light in an anticlockwise direction. The pair are enantiomers of each other which act as mirror images of each other and can also be known as optical isomers.

Any molecule that has a chiral carbon center can be either D or L isomer[2], however this system of naming molecules is fairly old and mainly used in regards to amino acids and carbohydrates in organic chemistry.

D-isomers mainly naturally occur in sugars while L-isomers tend to naturally be amino acids which makes the D and L naming system very effective in easily distinguishing between the stereoisomers[3].


  1. Medical dictionary, 2017, Available at : https://medical-dictionary.thefreedictionary.com/d-isomer 04/12/17
  2. Department of Chemistry, University of Maine, 2012, Available at: http://chemistry.umeche.maine.edu/CHY251/dlwrong.html 04/12/17
  3. Master Organic Chemistry, 2017, Available at: https://www.masterorganicchemistry.com/2017/05/24/d-and-l-sugars/ 04/12/17
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