Experiment 3:

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Experiment 3

• STEREOCHEMISTRY AND MOLECULAR MODELING OF
  CYCLOALKANES

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THE LAB REPORT

• This experiment is NOT in the current edition of
  the lab manual.
• Each student should print a copy of the FINAL LAB
  REPORT sheet accessible on the Blackboard Learn
  course website and bring it to lab to complete.
• Molecular model kits will be provided for
  assistance, or students can bring their own to
  lab.
• There is no other PRE lab or POST lab assignment
  for this experiment, just the completion of the
  FINAL LAB REPORT sheet.

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OBJECTIVES

• To practice drawing cyclohexane rings in chair
  conformations, and learn how to recognize axial
  and equatorial positions.
• To practice drawing monosubstituted and
  disubstituted cyclohexane rings in both chair
  conformations.
• To learn how to compare the stability of chair
  conformations, and identify which conformer is
  favored at equilibrium.

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THE LAB REPORT
Fill in the blanks using a single term from the
list at the top. Use textbook for assistance if
necessary.
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How to Draw Cyclohexane
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THE LAB REPORT
Follow instructions given for all problems.
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How to Draw the Axial and Equatorial Hydrogens
SUMMARY All substituents are drawn like this
2. Draw all equatorial positions as pairs of
parallel lines.
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THE LAB REPORT
Follow instructions given for all problems.
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Conformational Mobility of Cyclohexane-Ring Flips
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Conformations of Monosubstituted Cyclohexanes

• Although ring-flip occurs rapidly, the two
  conformers are not EQUAL!

This conformer has more diaxial interactions,
therefore is higher in energy!
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1,3-Diaxial Interactions

• Q What causes the difference in energy between
  the conformers?
• Steric strain due to 1,3-diaxial interactions.
• Q What is a 1,3-diaxial interaction?
• Atoms on C1 are too close to those on C3 and C5!

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Drawing Both Chair Conformations
Monosubstituted rings
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THE LAB REPORT
Follow instructions given for all problems.
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Drawing Both Chair Conformations Disubstituted
rings
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THE LAB REPORT
Follow instructions given for all problems.
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Conformational Analysis of Disubstituted
Cyclohexanes

• Q What is conformational analysis?
• Assessing energy of cycloalkane by summing all
  steric interactions.
• Q Why is it important?
• Can help predict which conformations are more
  favorable and more likely to exist.

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THE LAB REPORT
Follow instructions given for all problems.
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THE LAB REPORT
This table is given on the last page of the lab
report
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OVERVIEW

• Review concepts.
• Draw a chair conformation of cyclohexane.
• Draw and label axial and equatorial positions on
  a chair conformation of cyclohexane.
• Draw chair conformation of monosubstituted
  cyclohexane before and after ring flip.
• Draw chair conformations of disubstituted
  cyclohexanes before and after ring flip.
• Compare stability of chair conformations and
  predict major conformer.

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Just a suggestion

• BRING YOUR TEXTBOOK WITH YOU TO LAB!
• (IT MAY HELP ?!)