Chapter 5: Stereoisomers
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What is an isomer?
Molecule with the same molecular formula, and a different structure
What is a constitutional isomer?
Molecule with the same molecular formula, but different connectivity
What is a stereoisomer?
Molecule with a different orientation in space
What are the types of stereoisomers?
• cis and trans • conformations (rotating around a sigma bond) • mirror image isomers (enantiomers and diastereomers)
Achiral
Identical (superimposable) to its mirror image
Chiral
Nonsuperimposable to its mirror image
Enantiomers
Each isomer of a mirror image
Stereocenter
Source of chirality (carbon w 4 different substituents)
Diastereomer
Nonsuperimposable non-mirror image
Formula for number of possible stereoisomers
2^x (# of stereocenters)
Something that is optically active Is …
Chiral
Enantiomers have identical physical properties, such as…
boiling point, melting point, density
How do we tell enantiomers apart?
Plane polarized light, performed by a polarimeter
What is the specific notation for optical rotation?
[d]
How do enantiomers rotate light?
In equal and opposite directions
(+) Detrorotatory
Right/clockwise
(-) Levoratatory
Left/counter clockwise
What does optical rotation tell us?
How pure our sample is (optical purity)
What is produced when no optical rotation is present?
50-50 mix of enantiomers; known as a racemic mix
If one enantiomer is present, it is referred to as …
Enantiopure
What is it called if enantiomer is in excess (ee)?
Enantiomeric Excess (xs)
There is no correlation between optical rotation and …
Structure
Rectus
Right or clockwise
Sinister
Left or counterclockwise