Challenge: explain enantiomers to someone who is not a chemist!
Same chemical and physical properties in achiral environments.
A mixture of these cannot be separated by normal GC or HPLC techniques
Different chemical and physical properties in chiral environments.
A mixture of these can (theoretically) be separated by chiral GC or HPLC techniques
Different physical/chemical properties in chiral/achiral environments.
Naproxen An Over-the -Counter Chiral Auxillary
Brinkman, J. A., Sowa, J. R., Jr. In Catalysis of Organic Reactions, Herkes, F. E., Ed., Marcel Dekker: New York, 1998, p. 543 - 549.
Stereogenic center (stereocenter)- a point in a molecule bearing groups such that an interchange of any two groups will produce a stereoisomer.
Number of possible stereoisomers = 2n , n = # of stereocenters.
For Crixivan determine # possible stereoisomers?
Relative vs. Absolute Configurations
Relative configuration - 3-D structure is not known but it is known that one structure is the mirror image of the other.
(+) or d - dextrorotatory - cpd that rotates light to the right.
(-) or l - levorotatory - cpd that rotates light to the left.
(±) - racemic mixture - 1:1 mixture of (+) and (-) cpds, zero rotation.
Absolute configuration - 3-D structure is known.
R, S Nomenclature
Always draw the arrow on paper as you mind can easily reverse itself!
Shortcut: if lowest priority group is unambiguously in the front then reverse assignment.
Draw the structure of (S)-penicillamine (used for treatment of arthritis):
How many stereocenters are present; label each stereo center as R/S:
Reading Fischer Projections
Groups along the horizontal plane are facing forward. Groups along the vertical plane are facing back.
Haworth Projections - good for cyclic compounds.
E/Z Nomenclature - It's E/Z!
1. Split double bond in half.
Z - zusammen (together) - highest priority groups are on the same side.
Inversion of Configuration
SN2 reactions are an excellent example of reactions that go with inversion of configuration.
Retention of Configuration
Epimerization - a form of racemization
May occur with enolizable carbons:
Separation of Enantiomers
A) Pasteur's Method