Crash Course Organic Chemistry: Stereochemistry and Chirality

Introduction

• Crash Course Organic Chemistry hosted by Deboki Chakravarti.
• Discusses the concept of chirality and stereochemistry in organic molecules.

Story of Dr. Gilbert Levin

• 1990: Attempt to detect life on Mars using D-glucose and L-glucose.
• Key Finding: Humans can't digest L-glucose due to lack of enzyme recognition.
• Implication: Structure affects chemical behavior; stereochemistry is critical.

Importance of Molecular Shape

• Shape is crucial in biology, chemistry, and biochemistry.
• Isomers: Molecules with same parts but different arrangements.
  • Constitutional Isomers: Different connections between atoms.
  • Geometric Isomers: Different spatial arrangements due to double bonds.

Stereoisomers

• Same atom connections, different spatial arrangements.
• Example: Mirror images of sunglasses can be superimposable or non-superimposable.

Chirality

• Non-superimposable mirror images are chiral.
• Chirality Center: Carbon with four different groups attached.
  • Example: Butan-2-ol has a chiral center.

Drawing Enantiomers

• Steps:
  • Draw molecule and mirror image.
  • Solid wedges come out, dashed wedges go away.
• Example: Albuterol, a medication with one chiral center.

Naming Enantiomers

• Cahn-Ingold-Prelog Convention: Assign priorities (R/S system).
  • Priority based on atomic number.
  • Example: Butan-2-ol (2R)-butan-2-ol and (2S)-butan-2-ol.

Practicing Chirality Assignment

• Using 3D models for visualization.
• Example: Assigning R/S to albuterol enantiomers.

Cyclic Compounds and Chirality

• Example: Methylcyclopentane is achiral (superimposable mirror images).
• Internal Plane of Symmetry: Indicates achirality.
• Example: 2-Methylcyclopent-1-ene is chiral.

Molecules with Two Chiral Centers

• Notation: Use numbered carbons to specify R/S of chiral centers.
• Example: (3R,4S)-4 bromohexan-3-ol.
• Achirality Check: Superimposable mirror images and symmetry.

Rapid Fire Problems

• Decide if molecules are chiral or achiral using a flowchart.

Conclusion

• Stereochemistry is pivotal in organic chemistry.
• Future topics: Properties of enantiomers, light interaction, drug safety.

Support

• Crash Course Organic Chemistry is supported by Patreon.