1. Chapter 7 STEREOCHEMISTRY

2. CHIRALITY AND ENATIOMERS
Chiral Object – an object that IS NOT superimposable with its mirror image.
Achiral Object – an object that IS superimposable (i.e. identical) with its mirror image.
Enantiomers – stereoisomers, which are non-superimposable mirror images.
Stereochemistry

3. CHIRAL CARBON ATOMS
Chiral Carbon Atoms – carbon atoms bonded to FOUR DIFFERENT groups. Chiral atoms are generally called chirality centers. * *
mirror
Some rules:
If a molecule has NO chirality center, it is usually, but not necessarily achiral.
If a molecule has just ONE chirality center, it is definitely chiral.
If a molecule has MORE THAN ONE chirality center, it may or may not be chiral.
Stereochemistry

4. THE MIRROR IMAGES OF CARBON CENTERS WITH THREE DIFFERENT SUBSTITUENTS ARE SUPERIMPOSABLE
IDENTICAL WITH THE ORIGINAL
Stereochemistry

5. THE MIRROR IMAGES OF CARBON CENTERS WITH FOUR DIFFERENT SUBSTITUENTS (CHIRAL CARBON ATOMS) ARE NOT SUPERIMPOSABLE
120o * * *
mirror
NOT IDENTICAL WITH THE ORIGINAL
Stereochemistry

6. CARBON CENTERS WITH FOUR DIFFERENT SUBSTITTUENTS (CHIRAL CARBON ATOMS) DO NOT HAVE INTERNAL MIRROR PLANES OF SYMMETRY
Stereochemistry

7. CHIRAL COMPOUNDS ALSO DO NOT HAVE INTERNAL MIRROR PLANES OF SYMMETRY
MIRROR IMAGE IDENTICAL WITH ORIGINAL
MIRROR IMAGE IS NOT IDENTICAL WITH ORIGINAL
Stereochemistry

8. THE CAHN – INGOLD – PRELOG CONVENTION
Assign a “priority” and a number to each group, bonded to the chiral carbon atom. Highest priority group gets number 1, second in priority – number 2, third in priority – number 3, lowest in priority – number 4.
Orient the molecule in a fashion such that the lowest in priority group (number 4) is in back and view the molecule along the bond from the chiral center to group #4. Draw a curved arrow, starting from #1, through #2, to #3. If the arrow points in a clockwise direction – R-enantiomer, if the arrow points in a counter-clockwise direction – S-enantiomer.
Stereochemistry

9. THALIDOMIDE: DISASTROUS BIOLOGICAL ACTIVITY OF THE “WRONG” ENANTIOMER
Stereochemistry