Lecture on Enantiomers and Their Physical Properties

Introduction to Enantiomers

• Definition: Enantiomers are mirror image isomers.
• Physical Properties: They have nearly identical physical properties:
  • Boiling Point
  • Melting Point
  • Density
  • Refractive Indices

Biochemical Significance

• Distinction: Biomolecules can distinguish between enantiomers.

Example 1: Methadone

• Function: Methadone is an analgesic.
• Chiral Center Identification:
  • Find the sp3 hybridized carbon with four different groups.
  • Methadone’s chiral center is identified in the structure provided.
• Activity:
  • The R enantiomer is significantly more active than the S enantiomer.
• Drawing the R Enantiomer:
  • Assign priorities: Nitrogen (highest), Carbon-containing group (second), Methyl group (third).
  • Clockwise rotation indicates the correct R enantiomer.

Example 2: Albuterol

• Function: Albuterol is a bronchodilator.
• Chiral Center Identification:
  • Determine the chiral center in the given structure.
• Activity:
  • Only the R enantiomer is active.
• Drawing the R Enantiomer:
  • Assign priorities: Hydroxyl group (1), Nitrogen-containing group (2), Arine-containing group (3).
  • Clockwise rotation confirms the R enantiomer.

Detection of Enantiomers

• Polarimetry: A method using plain polarized light to distinguish enantiomers.
  • Plain Polarized Light: Vibrates in a single plane (e.g., up and down).
  • Optical Activity: Substances that rotate plain polarized light are optically active.
  • Enantiomers’ Effect:
    • Rotate light by the same amount but in opposite directions.

Racemic Mixtures

• Definition: Contains a 50-50 mixture of R and S enantiomers.
• Optical Rotation: Zero, as rotations cancel each other out.