absolute and relative configuration

1. Stereochemistry of
organic compounds
Optical isomerism: configuration

2. Configuration of optically active
compounds
• Relative configuration
• Absolute configuration

3. Relative configuration
• D and L configuration
• Relative to glyceraldehyde
• if the OH on the bottom chiral centre points to the right,
it is referred to as D-
• if the OH on the bottom chiral centre points to the left,
it is referred to as L-

5. • D and L is different from d and l
• D and L = configuration
• d/l = +/- = optical rotation
• A molecule with D configuration can be dextro or
laevo
• A molecule with L configuration can be dextro or
laevo

6. Absolute configuration
• R and S system
• The Cahn-Ingold-Prelog R/S rules are used for naming
enantiomers and diastereomers
• Steps:
• Identify the chirality centers
• Assign the priority to each group
• Position the lowest priority group away from viewer
• For the other 3 groups, determine the direction of high to low
priority (1 to 3)
• If this is clockwise, then the center is R (Latin: rectus = right)
• If this is counter clockwise, then it is S (Latin: sinister = left)

7. Priority of groups
1
• Higher atomic number, higher priority
2
• Higher mass number
3
• Atoms/ groups attached
• Double bonds are duplicated