Lecture Notes: Stereoisomers and Conformational Isomers

Introduction to Stereoisomers

• Definition: Stereoisomers are structures with the same structural formula, meaning the same connectivity between atoms, but with different spatial arrangements.
• Types of Stereoisomers:
  • Configurational Isomers
  • Conformational Isomers (focus of this lecture)

Conformational Isomers

• Definition: Forms of the same molecule with different conformations due to rotation around a sigma bond (a single bond).
• Characteristics:
  • Free rotation around a single bond allows for different molecular forms.
  • Interconversion among forms without breaking bonds.
  • Multiple forms exist simultaneously in a sample.

Example: 1,2-Dichloroethane

• Conformations:
  • Different arrangements due to rotation around carbon atoms.
  • Visualized using a projection along the carbon-carbon bond.
• Projections:
  • First Conformation: Chlorine atoms are opposite each other (energetically favorable due to large size of chlorines).
  • Second Conformation: Chlorine atoms are adjacent (less energetically favorable).
• Energy Considerations:
  • More time is spent in the energetically favorable conformation.
  • All conformations exist due to free bond rotation.

Example: Cyclohexane

• Structure: Six carbon ring (cyclic structure).
• Conformations:
  • Boat Conformation: Resembles a boat shape.
  • Chair Conformation: Resembles a chair shape, more common due to energy stability.
• Model Kits:
  • Useful for visualizing and understanding interconversion between conformations without breaking bonds.

Summary

• Conformational Isomers are constantly interconverting forms of a molecule due to single bond rotations.
• Understanding these isomers helps predict molecular behavior and energy stability.

End of lecture notes. Stay tuned for the next video lecture.