Lecture_Slides_Feb5_2025

Page 1: Chirality Centers

  • Identify chirality centers in given molecules including:

    • HO

    • Cl

    • Br

    • Cl

    • Br

    • Ly

Page 2: Physical Properties of Enantiomers

  • Key Differences:

    • Enantiomers have identical physical properties (boiling point, melting point, density, solubility), except for:

      • Rotation of plane polarized light

      • Interactions with other chiral molecules

    • Diastereomers:

      • Exhibit different physical properties (bp, mp, etc.)

    • Racemic Mixtures:

      • Display differing properties from each enantiomer, particularly solid-phase properties (e.g., melting point).

Page 3: Terms

  • Optically Active:

    • Definition: A sample that rotates plane polarized light

    • Example:

  • Optically Inactive:

    • Definition: A sample that does not rotate plane polarized light

    • Example: A 50/50 (racemic) mixture of enantiomers vs. a 60/40 mixture of pure.

Page 4: Chirality Definitions

  • Asymmetric Center (Chirality Center):

    • Definition: An atom that is a source of chirality; typically a tetrahedral atom (sp3) with four different substituents.

    • Example: Stereogenic center - any atom where switching substituents generates a different stereoisomer.

Page 5: Mirror Plane of Symmetry

  • Achirality versus Chirality:

    • A mirror plane is a sufficient but not necessary condition to demonstrate achirality.

    • Examples:

      • Structure can be achiral even with a lack of a mirror plane of symmetry.

Page 6: Stereogenic Centers Principles

  1. Reversing two substituents at a stereogenic center generates an alternate configuration.

  2. Reversing all configurations at asymmetric centers generates an enantiomer (or regenerates the original structure if achiral).

  3. Reversing some asymmetric configurations generates a diastereomer.

Page 7: Generation of Diastreomer Examples

  • Examples of Stereochemical Transformations:

    • Do not reverse cis/trans configurations in alkenes when generating enantiomers.

Page 8: Enantiomeric Resolution

  • Separation Techniques:

    • Use of diastereomeric salts with an enantiopure acid to separate racemic mixtures.

    • Example reactions with substrates NH2, HO via NaOH/H2O for separation into enantiomers.

Page 9: E & Z Configuration (CIP System)

  • Determine E and Z configurations based on priority rules:

    • Examples:

      • (E)-1-bromo-2-chloro-1-fluoroethene

      • (Z)-1-bromo-2-chloro-1-fluoroethene

      • Stability differences noted between E and Z isomers.

Page 10: Stability of Alkenes

  • Stability Ranking:

    • Order of stability: tetrasubstituted > trisubstituted > disubstituted (trans) > disubstituted (cis) > monosubstituted.

  • Relative Energies (kcal/mol): Example values for stability differences.

Page 11: R & S Configuration (CIP System)

  • Configuration Assignments:

    • Identifying the stereocenters using priority rules from Chiral centers in various configurations labeled as R and S.

Page 12: Fischer Projections: R & S Assignments

  • Fischer Projection Examples for R & S:

    • Visual representation of chirality and stereochemistry for compounds through Fischer projections for complex molecules.