lecture recording on 26 February 2025 at 13.51.17 PM

Exam Preparation

• Practice Exams:

  • Take practice exams using notes and answer keys.

  • Collaborate with peers to solve problems together.

• Timing Strategy:

  • Simulate exam conditions by reducing your time limit to 40 minutes for a 50-minute exam.

• Key Focus: Ensure understanding of all problems presented in practice exams.

Conformational Isomers

• Definition: Conformational isomers are variations of a molecule achieved through rotation about single bonds.

• Visualization Tools: Utilize models to visualize molecular conformation and understand relative positions of atoms.

Drawing Newman Projections

• Newman Projection Concept:

  • Look down the bond between two carbons (e.g., Carbon 2 and Carbon 3).

  • Identify groups attached to these carbons by visualizing a 3D representation.

• Wedge and Dash Notation:

  • Use wedges (bonds coming out of the page) and dashes (bonds going into the page) to represent 3D conformations.

  • Ensure that the wedge and dash arrangement reflects the actual 3D arrangement.

Molecular Configurations

• Energy States:

  • Eclipsed conformations: Higher energy due to torsional strain from overlapping electron clouds.

  • Staggered conformations: Lower energy, more stable due to minimized steric hindrance.

• Key Interactions:

  • Count eclipsing interactions between larger groups and determine energy stability.

  • Factors influencing energy: Number of eclipsing interactions and the size of the involved groups.

Energy Comparisons

• Relative Energies: Staggered conformations are generally more stable than eclipsed conformations.

• Count the number of eclipsing interactions (ignore hydrogen interactions) and compare sizes of eclipsing groups to evaluate stability.

  • Larger groups increase steric strain and raise energy levels.

Steric Interactions

• Gauche vs. Anti:

  • Fewer gauche interactions (groups close together) lead to lower energy states.

  • More anti interactions (groups opposite each other) reduce steric hindrance and lower the energy further.

• Lecture Example: Use of toy cats to explain the concept of steric hindrance and interactions within molecules.

Isomer Types

• Types of Isomers:

  • Constitutional isomers: Same molecular formula but different connectivity.

  • Stereoisomers: Same connectivity but differ in spatial orientation.

    • Enantiomers: Non-superimposable mirror images.

    • Diastereomers: Not mirror images and differ at one or more chiral centers.

Chiral vs. Achiral Molecules

• Chirality Defined: A chiral molecule lacks a plane of symmetry, leading to non-superimposable mirror images.

  • Example: Hands are chiral; cannot overlay.

  • Physicochemical implications for biological activity (e.g., drugs).

• Achiral Molecules: Have symmetry, allowing for superimposable mirror images.

  • Example: Can cut molecules into equal halves without transforming the structure.

Real-Life Examples of Chirality

• Thalidomide: Difference between enantiomers can lead to drastically different biological effects in humans.

• Olfactory Examples: Different smells from stereoisomers (e.g., spearmint vs. caraway) due to three-dimensional differences impacting receptor interactions.

• Visualizing Models: Emphasis on physical models and finger motions to understand molecular interactions and configurations.