Organic Chemistry 1

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Organic Chemistry 1

• Autumn 2004
• Problem Set 6 Solutions

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• More exotic solutions include

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• Eclipsed form of ethane 1,2-diol

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• Gauche staggered form of
• 1,2-dibromobutane focussing on the C1-C2 bond

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• gauche staggered form of 1,2-dibromoethane

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• eclipsed form of propane, focussing on the C1-C2
  bond

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• anti-staggered form of 2,3-dibromobutane,
  focusing on the C2-C3 bond

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• We can adopt the same strategy for the other two
  examples
• Do a switch to get the lowest priority group at
  the top of the diagram
• This also changes the absolute configuration
• Get the configuration of the altered molecule in
  the usual way
• 1 to 2 to 3 clockwise R
• 1 to 2 to 3 counterclockwise S

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• Draw both chair forms of the following molecules
  predict which will be the more stable

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• Key points
• Axial bonds must be vertical
• Bonds to equatorial substituents, should be
  roughly parallel to the opposite side of the ring
• When the ring is flipped, all axials become
  equatorial and vice versa

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• What stereoisomers would you expect for the
  following compounds? Label chiral centers R or S.
  Distinguish enantiomers and diastereoisomers.
  Which stereoisomers would you expect to be
  optically active?

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• In CCl4 the OH stretching frequency of A is
  independent of concentration, but in B it varies
  considerably, going from 3650 cm-1 at 0.03 M to
  3300 cm-1 at 1.0 M

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• For B we see non H-Bonded OH at 3650 cm-1, and
  H-bonded OH at 3300 cm-1. The relative
  intensities of these two bands vary with
  concentration.
• In A there is an intramolecular hydrogen bond,
  which is maintained irrespective of
  concentration.

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