chirality

• Isomers


  Molecules with the same molecular formula but different structures
• Enantiomers


  • Nonsuperposable mirror images
  • Chiral (show handedness)
• Stereocenter


  Carbon with four different groups bonded to it
• Achiral


  • Objects that are superposable on their mirror images
• Assigning R/S configuration


  1. Arrange groups in order of priority (based on atomic number)

  2. Orient molecule so lowest priority group is away from you

  3. Read 3 highest priority groups in order (clockwise = R, counterclockwise = S)
• Diastereomers


  Stereoisomers that are not mirror images
• For a molecule with n stereocenters, the maximum number of possible stereoisomers is 2^n
• Plane-polarized light


  Light waves vibrating only in parallel planes
• Polarimeter


  Instrument for measuring the ability of a compound to rotate the plane of plane-polarized light
• Optically active


  Showing a compound is capable of rotating the plane of plane-polarized light
• Dextrorotatory


  Clockwise rotation of the plane of plane-polarized light
• Levorotatory


  Counterclockwise rotation of the plane of plane-polarized light
• Specific rotation


  Observed rotation of an optically active substance at a concentration of 1 g/mL in a sample tube 10 cm long
• Except for inorganic salts and a few low-molecular-weight organic substances, the molecules in living systems, both plant and animal, are chiral
• Almost invariably only one stereoisomer is found in nature, though instances occur where more than one stereoisomer is found but they rarely exist together in the same biological system

  
• Enzymes


  • Protein biocatalysts that have many stereocenters
  • Only one stereoisomer is produced and used by any given organism
  • React with only substances that match their stereochemical requirements

  
• A molecule and its enantiomer or one of its diastereomers elicit different physiological responses in living systems