Study Set Content:
- A molecule that is not identical to its mirror image
Chiral
- Molecules that do not have a plane of symmetry and are not superimposable on their mirror image
Chiral
- Cause of chirality is the
presence of a carbon atom bonded to four different groups - e.g Hand, lactic acid
- Molecules with a plane of symmetry that is the same as its mirror image
Achiral
- Point in a molecule where 4 different groups are attached to carbon; it is the cause of chirality
Chirality Center or Steriocenter
Another way to identify a chiral molecule is to look for the presence of a
plane of symmetry.
The study of chirality originated in the early 19th century during the investigations by Jean-Baptiste Biot in the early 19th century investigated nature of plane polarized light
Optical Activity
Optically active substance that rotates the plane of polarization of plane-polarized light in counterclockwise direction
Levoratory
Optically active substance that rotates the plane of polarization of plane-polarized light in clockwise direction
Dextrorotatory:
Cahn-Ingold-Prelog rules
Rule #1
- Look at the four atoms directly attached to the chirality center, and rank them according to atomic number
- Atom with highest atomic number has highest ranking, and atom with lowest atomic number has lowest ranking
Rule #2
- If a decision cannot be reached by ranking the first atoms in the substituent, look at the second, third, or fourth atoms until the difference is found
Rule #3
- Multiple-bonded atoms are equivalent to the same number of single-bonded atoms
If the ranking (1-2-3)
R configuration:
Configuration of chirality center if the curved arrow is drawn clockwise
R-configuration
Configuration of chirality center if the curved arrow is drawn counterclockwise
S-configuration
Exact 3-D structure of a chiral molecule
Absolute configuration
- These are stereoisomers that are not mirror images.
Diastereomers
- have opposite configurations at ALL chirality centers
Enantiomers
have opposite configurations at SOME (one or more) chirality centers but the same configuration at others.
Diastereomers
compounds in which two diastereomers differ at only one chirality center but are the same at all others
Epimers
