Organic Chemistry: Chair Conformations

Introduction to Chair Conformations

• Discussed using the example of one methylcyclohexane.
• Importance of hydrogens in molecule configurations.
• Initial assumption: equal energy of hydrogens, but real configuration is different.

Tetrahedral Carbon Bond Angles

• Tetrahedral carbon bond angles are 109.5 degrees.
• Chair conformation allows maintaining the 109.5-degree bond angle.
• Violating the standard bond angles affects energy and stability.

Understanding Chair Conformations

• Chair conformation resembles a "Lazy Boy" recliner.
• Each carbon in the chair conformation can be labeled sequentially (1-6).
• Visualization of chair conformation helps in remembering structure.

Axial and Equatorial Bonds

• Axial Bonds:
  • Each carbon has one axial bond.
  • Bonds alternate up and down across carbons.
• Equatorial Bonds:
  • Not straight up or down, slightly angled.
  • Provides stability by maintaining bond angles.

Stability of Positions

• Equatorial positions are more stable than axial positions.
• 1,3 Axial Strain:
  • Occurs when substituents in axial positions cause steric clash.
  • Equatorial substituents avoid steric clash, thus more stable.

Drawing Chair Conformations

• Identify the largest substituent and prioritize its equatorial placement.
• Methyl and ethyl groups' arrangements impact stability.
• Ring Flip: Chair conformations can flip, changing axial and equatorial positions.

Application in Multiple Substituents

• Determine largest group for equatorial placement.
• Position other substituents to match molecular patterns.
• Examples with methyl, ethyl, isopropyl, and fluorine groups.
• Tert-Butyl Group:
  • Does not undergo a chair flip due to steric hindrance.
  • Position it equatorially for stability.

Conclusion

• Practice drawing chair conformations and understanding flips.
• Remember, equatorial positions are more stable, especially for large groups.
• No chair flip for Tert-Butyl groups due to steric clashes.

Key Takeaways

• Equatorial positions are more stable.
• Largest groups should occupy equatorial positions.
• Understanding chair flips and stability is crucial in organic chemistry.

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Note: Code for this lecture is 'LAZYBOY', referencing the chair conformation analogy.