1. Stereoisomers
Molecules with the same molecular formula and connectivity but different 3-D arrangement of atoms
e.g. conformers – differ by rotation about C-C s bonds
Relatively easily interconverted by heat
e.g. cis-trans isomerism – not easily converted

2. Stereochemistry 1. Chiral molecules/enantiomers
a. The R,S nomenclature system
2. Molecules with >1 chiral centre
Diastereoisomers
Meso compounds
The Fischer nomenclature for sugars

3. Ranking Priorities: Cahn-Ingold-Prelog Rules (chapter 6.5 – p 182)
Must rank atoms that are connected at comparison point
Higher atomic number gets higher priority
Br > Cl > S > P > O > N > C > H
RULE 2
If atomic numbers are the same, compare at next connection point at same distance
Compare until something has higher atomic number
Do not combine – always compare

4. Dealing With Multiple Bonds:
RULE 3
Substituent is drawn with connections shown and no double or triple bonds
Added atoms are valued with 0 ligands themselves

5. Sequence Rules
Rule 1:
• Assign each group priority according to the Cahn
Ingold-Prelog scheme
• With the lowest priority group pointing away, look at remaining 3 groups in a plane
• Clockwise is designated R (from Latin for “right”)
• Counterclockwise is designated S (from Latin word for “left”)

6. Rule 2:
If decision can’t be reached by ranking the first atoms in the substituents, look at the second, third, or fourth atoms until difference is found
Rule 3:
Multiple-bonded atoms are equivalent to the same number of single-bonded atoms

7. Some facts about Enantiomers
A 50:50 mixture of two chiral compounds (R and S forms) not rotate light – is called a racemic mixture
Enantiomers have identical physical properties – difficult to separate them
Enantiomers have identical chemical properties in most reactions – unless reagents are themselves chiral
Overwhelming majority of non-biological reactions which produce chiral compounds result in a racemic mixture.
Most biological reactions however usually are stereospecific – reaction with only one enantiomer or produces only one enantiomer

8. Diastereomers Molecules with more than one chirality center
Stereoisomeric forms that are not mirror images are called diastereomers

9. Meso Compounds
A compound with chiral centers with a plane of symmetry is called a meso compound
A meso compound is achiral

10. Fischer Projections of sugar molecules – How to interpret Fischer Projections
From wikipedia