Chapter 5: Stereoisomerism (made from pearson book, updated version will be up soon, i hope)

1. Ch.5 Review

2. Finding stereogenic centers
• All you are looking for is 4 different groups

3. Determining Chirality
• Method 1: Internal line of symmetry
• Can only be used for rings
• Is there an internal line of symmetry
• Yes: achiral
• no: chiral

4. Determining Chirality

5. Determining Chirality
• Method 2: Mirror and flip
• Step 1: Draw a line on side of molecule
• Step 2: transcribe the molecule while flipping it over the y axis
• Step 3 turn the molecule by 180 degrees by the z axis

6. Practice
Determine chirality

7. S and R naming
• Step 1: look at atoms surrounding stereogenic
center and rank them according to atomic
number
• Step 2: If there is a tie from step 1, look at the
groups surrounding the atoms we just looked at.
Look for a difference in atomic mass.
• Repeat until we are done
• Rule: If the atoms are the same but they are
connected by pi bonds, each bond counts once

8. R and S naming continued
• Step 3: draw arrows from priority 1 to 2 and from
2 to 3
• If clockwise: R
• If counterclockwise S
• Step 4: If group 4 is in the front, switch the sign.
(S to R) (R to S)

9. R and S IUPAC naming
• If there is one stereogenic center
• (S)-rest of name
• If there are 2 or more stereogenic centers
• (1R,2S)-rest of name

10. Determining Relationships
• Step 1: Find the molecular formula
• Same: continue to next step
• Different: different molecules
• Step 2: Is connectivity the same?
• Yes: continue to next step
• No: constitutional isomers

11. Determining Relationships
• Step 3: Count the number of stereo genic centers
• O= identical molecules
• 1?
• Identical chiral center= identical molecules
• Different chiral center= enantiomer

12. Determining Relationships
• 2 chiral centers?
• All the same: identical
• One or more different: Diastereomer
• All different: enantiomer
• If 2 chiral centers are symmetric and opposite they are meso
compounds

13. Practice
Determine the
relationship of each
set of molecules

14. Types of stereoisomers
• Meso compounds
• Achiral
• Have an equal number of opposite signs
• Enantiomers are nonsuperimposable mirror images
• Diastereomers are not mirror images

15. Optical activity
• Dextrorotary (d)= += clockwise rotation
• Levoratory (l)= - = counterclockwise rotation
• Ee= enantiomeric excess= creates optical activity
• Achiral molecules and racemates are optically inactive
• Formula for ee
• Specific rotation formulas
• Observed rotation formula