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Cyclohexane Derivatives Review

• The class previously discussed cyclohexane derivatives and chair conformations.

• Wedges and dashes indicate perspective:

• A wedge means the atom (like chlorine) is coming towards the viewer.

• A dash indicates the atom (like bromine) is pointed away.

• For each sp³ hybridized carbon in cyclohexane:

• Every carbon atom on the ring typically has two hydrogen atoms that are implied but not explicitly shown.

Chair Conformation Drawing Tips

• Representing a cyclohexane molecule on paper in a chair conformation requires pulling it out of the plane of the paper for a 3D perspective.

• Understanding axial (up/down) and equatorial (angled) positions is crucial:

• Draw axial lines for carbon atoms straight up or down.

• Equatorial lines are drawn at angles.

• Attention to directionality is essential during chair flips—only axial groups become equatorial and vice versa.

• Use visual aids like molecular model kits to conceptualize spatial relationships.

Conformational Analysis

• Any chair confirmation can be determined through a systematic approach:

• Start at a fixed carbon point, typically choosing Carbon 1.

• Maintain consistent numbering for clarity.

• Identify positions of axials and equatorials based on structural substituents carefully.

• Understand 1,3-diaxial strain: groups in these positions can lead to higher energy and less stability.

Stability Considerations

• When comparing two chair forms, the stability is dictated by how many substituents are axial.

• Generally, more equatorial groups mean a more stable conformation due to lower steric strain.

• Recognize larger alkyl groups prefer equatorial positions to minimize steric hindrance.

Introduction to Stereochemistry

• Topic 5 will cover stereochemistry—how the spatial arrangement of atoms affects properties.

• Two molecules may have the same molecular formula and connectivity but differ in stereochemical arrangements, leading to different physical and chemical properties.

• Key distinction will entail identifying cis (same side) versus trans (opposite sides) configurations of substituents on rings.

• Understanding stereochemistry is critical for implications in reactivity and medicinal chemistry.