Class Overview

• Discussed active drama regarding a technical issue with question number seven, awarded full credit due to problems.
• Apologized for any inconvenience experienced by the students on the assignment.
• Announced the class agenda focusing on cyclohexanes and beginning stereochemistry.

Cyclohexanes

Previous Discussions

• Reviewed drawings assigned as warm-ups for questions six and seven.
• Recommended to position wedges and dashes accurately for clarity in molecular representation.

Practice with Cyclohexanes

• Emphasized the importance of numbering the cyclohexane ring for clarity:
  • Can number starting from any carbon, but must maintain consistency (e.g., counterclockwise or clockwise).
  • Highlighted relation between axial and equatorial positions and their significance when determining stability.
  • Example Question:
  • Carbon 1 has a group that is equatorial (coming off up), and an axial bond going down.
  • If both axial or equatorial, check if groups are cis or trans by evaluating wedge and dash orientations:
  • Example: One wedge and one dash signifies trans; both equal indicates cis.

Chair Flips

• Explained the concept of chair flipping:
  • All axial positions change to equatorial and vice versa, but the up/down configuration remains the same.
  • Example activity:
  • Grab carbon 1 and pull it down, while grabbing carbon 2 and pulling it up to visualize the chair flip process.
  • Discussed axial and equatorial methyl groups:
  • Importance of accurately drawing and flipping to see energy conformations and stability.

Stability of Cyclohexanes

Assessing Stability

• Methyl groups in equatorial positions are preferred due to reduced steric interactions:
  • Stability assessment can be realized through NMR, indicating that 95% of methyl groups are equatorial.
  • Engaged in a discussion on steric strain, especially when methyls or larger groups are axial:
  • One-three diaxial interactions exponentially increase energy and reduce stability in axial scenarios.

Dimethylcyclohexane Examples

• Compare cis and trans isomers to see how functional group positioning affects stability:
  • Cis isomers (with one axial and one equatorial methyl group) are equally stable.
  • Trans isomers (both groups equatorial) are preferred because of lower steric strain compared to cis configurations.
  • Emphasized that stability depends on positioning; both equatorial methyls in a cis configuration can sometimes lead to increased stability.

Introduction to Stereochemistry

Conceptual Understanding

• Stereoisomers defined as having the same molecular formula and connectivity but differing in spatial arrangement:
  • Cannot interconvert through bond rotation.
  • Discussed importance of visualizing 3D structures in understanding stereochemistry.

Chirality

• Introducing chirality and achirality:
  • Chiral objects cannot be superimposed on their mirror images, while achiral can be.
  • Used hands as an example for non-superimposable mirror images and discussed real-life applications.

Simple Methyl Substitutions

• Activities in class involved identifying whether certain substitution patterns on methane were chiral or achiral:
  • Ongoing practical activities to reinforce understanding of chirality through visual comparisons of molecule configurations.

Additional Observations

• Discussed symmetry and its relationship to chirality:
  • Achiral objects possess a plane of symmetry, making identification straightforward.
  • Emphasized finding a plane of symmetry in various molecular configurations helps to quickly assess chirality status.

Future Topics

• Scheduled further in-depth discussion about stereochemistry and chirality in following classes.
• Confirmed that students should return all borrowed molecular models by the next class session.