1. Chapter 6 Principles of Stereochemistry ***Bring Your Model Kits to Class!***

3. Stereoisomers: compounds that have the same connectivity, but a different arrangement of atoms in space
Enantiomers: molecules that are non-superimposable (non-congruent) mirror images

4. Enantiomers

5. Enantiomers are said to be “chiral”
They possess the property of “chirality”
Greek: “hand” or “handedness”
No plane of symmetry

6. If a molecule is superimposable on its mirror image it is said to be “achiral”
Has a plane of symmetry

7. Chiral Carbons
Many chiral molecules contain one or more asymmetric carbons
Called “Chiral Carbons”
Attached to four different groups
Denoted by an asterisk
Source of stereoisomerism
Interchange of groups = other stereoisomer
Stereocenters

8. Problems
Identify, with an asterisk, the chiral carbons in the following molecules:

9. How do we differentiate between these two enantiomers
How do we differentiate between these two enantiomers? What do we call them?

10. Nomenclature of Enantiomers
Identify your chiral carbon
Prioritize your substituents on the chiral carbon according to the Cahn-Ingold-Prelog priority rules used to determine E and Z for alkenes
Highest priority = 1, Lowest Priority = 4

11. Priority Assignment Rules
Identify the atoms directly attached to the C and rank them according to atomic #.
Higher atomic # = higher priority
Higher isotopic mass = higher priority

12. If the first atoms connected to the chiral carbon are the same, continue moving outward until the first point of difference

13. Multiple-bonded atoms are equivalent to the same number of single bonded atoms

14. Point the lowest priority substituent away from you and look at the 3 remaining groups in a plane
Count  1, 2, 3
If you go CW = R
(rectus, Latin “proper”)
If you go CCW = S
(sinister, Latin “left”)

16. Name your enantiomers by placing an “(R)-” or an “(S)-” in front of the molecule’s IUPAC name

17. Problems
Identify whether the following molecules are R or S.
Identify and name the following molecules: