chiral molecules
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Chiral Molecules. Chapter 12.6. Definition of Isomer * Structural *. Molecules with the same formula but different structure and characteristics Example C 3 H 7 OH 1-propanol2-propanol. Definition of Isomer * Stereoisomers/Enantiomers *. - PowerPoint PPT PresentationTRANSCRIPT
Chiral Molecules
Chapter 12.6
Definition of Isomer* Structural *
• Molecules with the same formula but different structure and characteristics
Example C3H7OH
1-propanol 2-propanol
• Molecules that have the same structural components but are mirror images from each other
• Like left hand, right hand or right shoe, left shoe
Definition of Isomer * Stereoisomers/Enantiomers *
Enantiomers of Molecules
• They do not match up…no matter how they are rotated
Rotated On Top
Biological Importance
• In the 3D environment of the body, enantiomers are considered two different molecules: only one version works! Like your
right glove doesn’t fit your left hand
Carbon Stereoisomers
• For carbon to form a stereoisomer – it has to bond to 4 different substituents
• Below: orange, purple, green and white
Carbon Stereoisomer
• If Carbon does not have 4 different substituents, it can be rotated and made to overlap…giving an identical molecule
Chirality
• A carbon with 4 different substituents is called a chiral carbon, often indicated by a *
• It can come in the form of two different enantiomers
Fischer Projection
• Molecular drawing that shows chirality• Chiral carbons are indicated as crosses
SH SH H OH HO H
NH2 NH2
Fischer Projection• Horizontal lines – forward bonds in 3-D model• Vertical lines – bonds that point away in 3-D
Mark all Carbons that are chiral
Which of the molecules are correctly drawn as Fischer Projections?
A B C CHO COOH COH
H3C H HO CH3 H3C OH CHO CHO OH No – not chiral
2 CHO attached to CYes
4 different substituentsNo – not chiral
2 OH attached to C
Drawing Rules for Fischer
• Molecular axis has to be vertical with highest oxidized Carbon on top
• All chiral carbons become crossed lines• Non-chiral carbons are written condensed• Draw the molecule below as a Fischer Projection
D and L Enantiomers
• The handedness of enantiomers is indicated as either L –Left or D- Right with reference to certain substituents
D and L Enantiomers• In larger carbohydrates, the hydroxyl furthest
from the top is used for D and L