1.4 Chirality: Handedness in Molecules

• Most biological molecules, including carbohydrates, exhibit the property of “handedness” (form of isomerism).
• 2 forms of handedness:

  1. "Left - handed" form
  2. "Right - handed" form
• Mirror image

  • Reflection of an object in a mirror.
• Classes of objects based on Mirror images:

  1. Superimposable
  2. Nonsuperimposable
• Superimposable

  • Images that coincide at all points when the images are laid upon each other.

  
• Nonsuperimposable

  • Images where not all points coincide when the images are laid upon each other.

  
• Chiral molecule

  • Has 4 different atoms bonded to 1 carbon.
  • Does not have an internal plane of symmetry.
  • Nonsuperimposable

  
• Achiral molecule

  • 3 or less different atoms bonded to 1 carbon atom.
  • Has a plane of symmetry
  • Superimposable