1. Chapter 5: Stereochemistry
CH 5-1 Introduction
Isomer Review (Constitutional vs Stereoisomers)
Chirality
Chiral Carbon (chiral centers)
Enantiomers: mirror-image stereoisomers
Drawing Stereoisomers: zig/zag structures
Stereochemistry Nomenclature: R,S configurations
Diastereomers and Meso compounds: molecules with multiple chiral centers; Fisher Projections.
Stereoisomers in cycloalkanes
Properties of Chiral Molecules

2. Isomer Update
(geometric)

3. Chirality
Chiral objects (and molecules) have no plane of symmetry and can not be superimposed on their mirror images……
Huh?

4. Chirality “right “left handed” handed”
-helical sea shells are spiral, with either a right handed or left handed twist. Most are right helical.

5. Chirality
-Milky way galaxy

6. Chirality
Chiral molecules have no plane of symmetry and can not be superimposed on their mirror images
“B” form of DNA
“Z” form of DNA
-Double helical “B” DNA has a “right handed” twist, and is the most common form of DNA in solution.
-“Z” DNA is left handed.

7. Chirality Summary A B C D E F G H I J
Chiral molecules and objects have no plane of symmetry and can not be superimposed on their mirror images
Scissors
Pyramid
Basketball
Coffee mug (no printing)
Cylinder
Key
Baseball glove
Cell phone
A B C D E F G H I J
What about Carbon Atoms?

8. Chiral Carbon (Chiral Center)
Chiral carbon (chiral center) must be sp3 hybridized (tetrahedral)
Must have 4 different atoms or groups bonded to it (no plane of symmetry)
Stereoisomers: Molecules with the same formula and connectivity, but are not superimposable (different 3-D connectivity).
Spearmint
Caraway

9. Chiral Organic Molecules Enantiomers: Mirror-Image Stereoisomers
A chiral molecule must have at least one sp3 chiral carbon.
Enantiomers: A pair of stereoisomers that are non-superimposable mirror images (easier definition coming).

10. 2-D structure:
Draw accurate 2-D and 3-D zig-zag line structures for 3-chloro-4-ethyl hexane: ●
3-D structures (chiral center only): ● ●
These two molecules represent a pair of Enantiomers.
These are mirror image Stereoisomers, i.e., two positions to the chiral carbon (Cl & H) have switched.
Enantiomers have identical physical and chemical properties.