Chiral vs Achiral: Understanding Molecular Chirality

Introduction

• Chiral Molecules: Non-superimposable on their mirror images, similar to left and right hands.
• Achiral Molecules: Superimposable on their mirror images.

Key Concepts

Chiral Molecules

• Derived from the Greek word "cheir" meaning "hand".
• Chirality: The geometric property where molecules are non-superimposable on their mirror images.
• Stereochemistry: Chiral molecules exist as two stereoisomers known as enantiomers.
  • Enantiomers: Non-superimposable mirror images, classified into right-handed (dextrorotatory) and left-handed (levorotatory).
  • Properties: Identical chemical properties unless interacting with another chiral species, similar physical properties.
  • Racemic Mixture: A 50:50 mixture of two enantiomers showing distinct properties.

Achiral Molecules

• Superimposable on their mirror images.
• Have a plane of symmetry or a center of symmetry.
• Meso Compounds: Achiral molecules with stereocenters.
  • Examples include (meso)-2,3-dibromobutane and trans-1,2-dichloro-1,2-ethanediol.

Differences Between Chiral and Achiral Molecules

Enantiomers

• Definition: Pairs of molecules that are non-superimposable mirror images.
• Properties: Similar melting and boiling points.
• Identification: By passing plane-polarized light through them.

FAQs

1. What are chiral molecules?
   • Non-superimposable, lacking a plane or center of symmetry.
2. What are achiral compounds?
   • Superimposable, possess a plane or center of symmetry.
3. What is a racemic mixture?
   • A mixture of two enantiomers with unique properties.
4. What is an enantiomer?
   • Molecules with non-superimposable mirror images.
5. Are chiral and achiral molecules identical?
   • No, they differ in superimposability and symmetry.