Ch 5 Stereochemistry Flashcards
Stereoisomer vs Constitutional Isomer
Constitutional Isomer - Same chemical makeup, different arrangement
Stereoisomer - Same arrangement, different position IN SPACE (orientation)
Stereoisomer
Molecule with same chemical arrangement, but different orientation
Achiral vs Chiral
Achiral - identical to mirror image, SUPER IMPOSABLE
Chiral - non-superimposable to mirror image
Enantiomers
Each isomer of a mirror image
Stereocenter
Source, or center, of chirality.
ie. A carbon w/ 4 DIFFERENT substituents is often a stereocenter
Diastereomer
Non-super imposable, non-mirror image stereoisomer.
Why is it hard to tell Enantiomers apart?
How do you tell them apart?
Enantiomers have IDENTICAL physical properties (boiling point, melting point, density)
They have different OPTICAL ACTIVITY. Enantiomers rotate light in EQUAL and OPPOSITE directions.
Optical Activity
If something is optically active, it is CHIRAL. It redirects light passing through it differently.
Specific Rotation Equation
(alpha)/(length of sample cell)(concentration in g/mL)
Dextrorotatory
Optically turns light RIGHT or CLOCKWISE (+)
Levorotatory
Optically turns light LEFT or COUNTERCLOCKWISE (-)
What can optical rotation tell us about a sample?
Can determine optical purity of sample
Racemic Mixture
50:50 mix of enantiomers. Optical purity=0
Enantiomeric Excess
One enantiomer is in excess in solution
Cahn-Ingol-Prelog Rule
Highest Atomic number takes priority in Absolute Config
