1. Isomers: The Arrangement of Atoms in Space University of California,
Chapter 4
Isomers: The Arrangement of Atoms in Space
Paula Yurkanis Bruice
University of California,
Santa Barbara

2. Contents of Chapter 4 Conformational and Configurational Isomers
Chirality Centers, Enantiomers
Optical Rotation
Isomers with More Than One Chirality Center
Separation of Enantiomers
Stereochemistry of Reactions
Chapter 6

3. Kinds of Isomers
Chapter 6

4. Conformational Isomers
Chapter 6

5. Configurational Isomers: Cis-Trans Diastereomers
Chapter 6

6. The E,Z System for Designating
Geometric Isomers

7. The E,Z System for Designating
Geometric Isomers

8. The E,Z System for Designating
Geometric Isomers
If the atoms attached to the sp2 carbon are the same, the atoms attached to the tied atoms are compared; the one with the greater atomic number belongs to the group with the higher priority.

9. The E,Z System for Designating
Geometric Isomers
If an atom is doubly bonded to another atom, treat it as if it were singly bonded to two of those atoms.
If an atom is triply bonded to another atom, treat it as if it were singly bonded to three of those atoms.
Cancel atoms that are identical in the two groups; use the remaining atoms to determine the group with the higher priority.

10. Isomers with One Chirality Center
A chirality center arises when four different substituents are bonded to a carbon
Only two isomers are possible, an R isomer and an S isomer.
Chapter 6

11. Chirality
R and S enantiomers are mirror images of each other, just as your right hand is the mirror image of your left hand
Chapter 6

12. Chirality
Any object that has a plane or point of symmetry is achiral (not chiral).
Chapter 6

13. Examples
chiral
achiral
Chapter 6

14. Mirror Trick
Whenever two structures can be positioned around a symmetry plane if they aren’t identical they’re enantiomers.
Chapter 6

15. Drawing Enantiomers Fischer Projections
N and S are down into plane, E and W are up out of plane of page or screen.
Chapter 6

16. Naming Enantiomers: The R,S System of Nomenclature
Rank groups by atomic number of the atom bonded to the chirality center. Use the same system that was used for the E and Z isomers of alkenes
Chapter 6

17. Naming Enantiomers: The R,S System of Nomenclature
Orient molecule so that group (or atom) of lowest priority is directed into plane.
3. Draw a curve from group of highest priority through the group of second priority to group of third priority
Chapter 6

18. Naming Enantiomers: The R,S System of Nomenclature
R (Latin rectus) = right turn
S (Latin sinister) = left turn 1 2 3 4
(S)-2-bromobutane
Chapter 6

19. Swap Trick
If for any reason you ever wish a group were in a different position simply swap it with another group.
Swap simply reverses the chirality.
R for switched compound implies S for actual compound
Chapter 6

20. Low Priority Group Up Trick
If the low priority group in figure points up rather than down simply draw circular arrow and reverse chirality.
R for reversed chirality implies S for actual chirality
Chapter 6

21. Rotation Trick
If one group is in the same position in two different structures and the other three groups are ALL in different positions then the structures are identical.
These 3 structures interconverted by rotation of bottom 3 groups around vertical bond attached to top group
Chapter 6

22. Compounds with More Than One Chirality Center
Two Pairs of Similar Groups
Chapter 6

23. Compounds with More Than One Chirality Center
Three Pairs of Similar Groups
Chapter 6

24. Meso Compounds
Chapter 6

25. Drill on Meso Compounds
Does the following compound have a stereoisomer that is a meso compound?
Plane of symmetry
Meso form possible
Chapter 6

26. Relative and Absolute Configurations
(–) amphetamine is known to have the R- configuration
Therefore the (+) form has S configuration
Chapter 6

27. Separation of Enantiomers
Racemic lactic acid can be reacted with a naturally occurring chiral base, such as morphine or strychnine
The product is a pair of diastereomers
Properties of diastereomers are sufficiently different from each other to allow separation
After separation, each diastereomer can be reacted with hydrochloric acid, yielding an optically pure R or S acid
Chapter 6

28. Reaction Stereochemistry
A regioselective reaction is one in which multiple constitutional isomers possible, but more of some formed than others.
Chapter 6

29. Syn Addition When the two substituents add to the same side
Addition of H2 is a syn addition
Chapter 6