R_S_Stereoisomerism - R/S Stereochemistry Chemistry 357 -...

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R/S Stereochemistry Chemistry 357 - Qatar Organic Chemistry for the Life Sciences Stereoisomerism and R/S Stereochemistry - Tutorial Stereoisomerism is one of the most important aspects of organic chemistry. It’s importance increases in magnitude as we move from simple organic chemistry to biological chemistry, biochemistry and human physiology. In the majority of instances, the molecules of biological systems (e.g. enzymes, regulator proteins, hormones, amino acids, sugars, etc.) have “ HANDEDNESS ” or CHIRALITY associated with their structures. In molecular terms, a molecule is said to be CHIRAL if it is non-superimposable on its mirror image. A real word analogy would be your shoes: although your left shoe is a mirror image of your right shoe, if you try to fit one into the other, you see that they are not identical. The biological repercussion is that if you place your left foot into your right shoe, it is not a comfortable fit. Molecules that are non- superimposable mirror images are referred to as ENANTIOMERS . Enantiomers have identical physical (bp, mp, IR, colour, etc) and chemical properties with two exceptions: 1) their ability to rotate plane polarized light and 2) their interaction with other chiral molecules. One of the most dramatic and unfortunate examples of the detrimental powers of not understanding “biological chirality” occurred in the late 1950s in Canada and Europe. The drug thalidomide was approved in these countries to treat morning sickness (nausea) in pregnant women. The drug was prescribed for hundreds of thousands of women over an eight-month period but it wasn’t until their babies were born with severe birth defects that the full extent of the problem with the drug was recognized. Thalidomide was sold as RACEMIC MIXTURE (equal mixture of two ENANTIOMERS ) and as it turned out, one enantiomer prevents nausea while the other is a severe teratogen (causes birth defects in developing fetus). Tens of
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This note was uploaded on 03/29/2009 for the course CHEM 3570 taught by Professor Ganem, b during the Fall '06 term at Cornell University (Engineering School).

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R_S_Stereoisomerism - R/S Stereochemistry Chemistry 357 -...

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