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Chirality

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Claire Hendershot

on 18 June 2013

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Transcript of Chirality

Claire Hendershot
June 15, 2013
1 B/D

Molecular Chirality
"chiral" = hand in Greek
What is chirality?
Chiral molecules are a type of
stereoisomer
.

They are non-superimposable mirror images.

A chiral atom and its mirror image are called
enantiomers.

Enantiomers share the same physical properties and the same chemical properties (in a chiral environment).
Handedness
Enantiomers can be right or left "handed".

In a solution, chiral substances can rotate a plane of polarized light. Such chiral molecules are
optically active.
Optical Activity in Action
Uses: polarized sunglasses
Racemic Mixtures
Solutions that contain R and S enantiomers in equal quantities are
racemic mixtures
.

They cannot rotate the plane of polarized light because the rotations of each enantiomer cancel each other out.

A chemical reaction that creates a chiral product will yield a racemate. This makes the production of a racemate cheaper and easier than that of a pure enantiomer.

Many substances, such as tartaric acid, are found in nature as pure enantiomers.

Many biological molecules, such as DNA, amino acids, and enzymes, are chiral.
Chirality of Biological Molecules
Enzymes are chiral catalysts. Their chirality contributes to the "lock and key fit" with their substrate.







All amino acids (except glycerine) are chiral.
All amino acids in proteins are "left handed".
This consistent chirality leads to the double helix structure of DNA.
carbon center bonded to four DIFFERENT atoms or groups of atoms
Chiral Lingo
The enantiomer that rotates light to the right is
dextroratory
and is labeled
"R"
The enantiomer that rotates light to the left is called
levorotatory
and is labeled
"S"
http://s3.photobucket.com/albums/y66/saviorknights/?action=view&current=opticalactivity.mp4
Many pharmecutical drugs consist of chiral molecules. When these drugs are administered as racemic mixtures, one enantiomer is beneficial and the other is inactive or harmful.

When a racemic mixture is placed in a chiral environment, the two isomers can be seperated.

Drugs can be synthesized in order to isolate a desired enantiomer. This enhances the efficiency of the drug and reduces or eradicates side effects. Such drugs are "enantiopure"
Why Chirality Actually Matters
Enantiopure Examples

Lunesta:

Eszopiclone (Lunesta) vs Zopiclone (Imovane)
These are active enantiomers. In the synthesis of Lunesta, it was found that one stereoisomer ("S") was effective, while the other was inactive. Doses of eszopiclone are half that of zopiclone and are cheaper.
Seractil:
Ibuprofin (Advil/Motrin) vs Dexibuprofin (Seractil).
Ibuprofin is a racemic mixture. Dexibuprofin is a single enantiomer.
Works Cited
Our chemistry book
http://www.chem.nottingham.ac.uk/PECD_ChiMol.phtml
http://www.ucd.ie/biocatal/biocatal/Chiral.html
http://chemwiki.ucdavis.edu/Organic_Chemistry/Chirality
Full transcript