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Surviving Chair Structures

Surviving Chair Structures. A “How-to” Review. Surviving Chair Structures …. Cyclohexane and what you should be able to do: Draw in 2-D , showing stereochem Transfer to a chair conformation Draw the chair flipped conformation

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Surviving Chair Structures

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  1. Surviving Chair Structures A “How-to” Review

  2. Surviving Chair Structures… Cyclohexaneand what you should be able to do: • Draw in 2-D, showing stereochem • Transfer to a chair conformation • Draw the chair flipped conformation • Identify the high or low energy conformation (or calculate the values, if I give you the table of values)

  3. Step 1: Cyclohexane in 2-D • 2 groups on the ring can be Cis (on the same side) or Trans (on opposite sides)

  4. Step 1: Cyclohexane in 2-D • 2 groups on the ring can be Cis or Trans: • Cis = Same Sides

  5. Step 1: Cyclohexane in 2-D • 2 groups on the ring can be Cis or Trans: • Trans = Opposite Sides

  6. Step 1: Cyclohexane in 2-D • Which is it? Cis or Trans?

  7. Step 1: Cyclohexane in 2-D • Answer: One Up… One Down… Trans…

  8. Step 1: Cyclohexane in 2-D • Which are they? Cis or Trans?

  9. Step 1: Cyclohexane in 2-D • How did you do?

  10. Step 2: Draw cis-1, 3-dimethylcyclohexane

  11. Step 2: Draw cis-1, 3-dimethylcyclohexane Start with a hexagon…

  12. Step 2: Draw cis-1, 3-dimethylcyclohexane … then pick a position to be #1 (and ANY position can be #1)…

  13. Step 2: Draw cis-1, 3-dimethylcyclohexane … then number around the ring (CW or CCW) to find #3(since you are drawing a 1,3-disubstituted ring)

  14. Step 2: Draw cis-1, 3-dimethylcyclohexane … then attach the necessary groups (two methyl groups, in this case) to the #1 and #3 positions you’ve decided to use…

  15. Step 2: Draw cis-1, 3-dimethylcyclohexane …then add stereochemistry to show the relative positions (cis = same side, trans = opposite sides). Since the compound is cis-1,3-dimethylcyclohexane, either of the answers below will be correct answers…

  16. Step 2: Draw cis-1, 3-dimethylcyclohexane … as would these, depending on where you placed your #1 and #3 positions…

  17. Step 3: Converting to a Chair structure

  18. Step 3: Converting to a Chair structure Chair structures are the 3-D representation of the cyclohexane ring… Remember that this view is from the side of the ring, not from above or below…

  19. Step 3: Converting to a Chair structure First – let’s remind ourselves about the different positions on a chair structure…

  20. Step 3: Converting to a Chair structure Every cyclohexane chair has six carbons, three that zig-zag up and three that zig-zag down… make sure you can identify them…

  21. Step 3: Converting to a Chair structure On the positions that zig-zag UP, you will find the vertical UP AXIAL positions… on the positions that zig-zag DOWN, you will find the vertical DOWN AXIAL positions…

  22. Step 3: Converting to a Chair structure On the positions that zig-zag UP, you will find the (semi-horizontal) DOWN EQUATORIAL positions… on the positions that zig-zag DOWN, you will find the (semi-horizontal) UP EQUATORIAL positions…

  23. Step 3: Converting to a Chair structure All of the positions are shown below in one structure:

  24. Step 3: Converting to a Chair structure All positions, together on the ring… make sure you can find them to draw them… Fill them in on the template shown… (answer on previous slide!)

  25. Step 3: Converting to a Chair structure Translation required: wedges (or bold lines) in 2-D are the “UP” positions and dashes in 2-D are the “DOWN” positions… Up is Up and Down is Down, regardless of axial or equatorial…

  26. Step 3: Converting to a Chair structure Recall that any position on the cyclohexane can be #1…

  27. Step 3: Convert to a Chair structure …and any position on the chair form can be #1…

  28. Step 3: Convert to a Chair structure …for practice and repetition’s sake (so you are less likely to make errors), choose your #1 on both and always stay in the same positions…

  29. Step 3: Convert to a Chair structure …for the purpose of this example, we will use the #1 position on the hexagon shown below…

  30. Step 3: Convert to a Chair structure …and this will correlate to the #1 position chosen here on this chair form… Remember that YOU can chose whichever #1 YOU want to use…

  31. Step 3: Converting to a Chair structure If this is #1 on the hexagon, number the ring accordingly… CW or CCW…

  32. Step 3: Converting to a Chair structure …then do likewise on the chair structure… again, CW versus CCW does not matter (its all RELATIVE to each other…)

  33. Step 3: Converting to a Chair structure …now you can see what carbons on the hexagon form of cyclohexane correlate to the chair form of cyclohexane…

  34. Step 3: Converting to a Chair structure Now let’s consider stereochemistry on the 2-dimensional version of cyclohexane…

  35. Step 3: Converting to a Chair structure Try This: Draw trans-1,4-dichlorocyclohexane in 2-dimensions… I numbered this one CW, just for fun…

  36. Step 3: Converting to a Chair structure How did you do? Your answer may not look exactly the same as the one below, but remember – its all RELATIVE… trans = one UP and one DOWN…

  37. Step 3: Converting to a Chair structure Now you have to convert this into a chair structure… Watch your UP’s and DOWN’s…

  38. Step 3: Converting to a Chair structure Position #1 has in this 2-D drawing an UP chloro group and position #4 has a DOWN chloro group…

  39. Step 3: Converting to a Chair structure Label position 1 and 4 on the chair structure you are using and then transfer the information. Position 1 has an UP chloro group and position 4 has a DOWN chloro group…

  40. Step 3: Converting to a Chair structure You need to fill in the groups on their positions (recall Axial and Equatorial positions). Position #1 has an UP chloro group and “up” on Position #1 will be AXIAL UP. Position #4 has a DOWN chloro group and “down” on Position #4 will be AXIAL DOWN.

  41. Step 3: Converting to a Chair structure Try it again: Draw cis-1-bromo-3-methylcyclohexane as a chair structure… Start in 2-D… Go ahead – before you move to the next slide… Note that this time I numbered CW…

  42. Step 3: Converting to a Chair structure Cis-1-bromo-3-methylcyclohexane, in 2-dimensions…

  43. Step 3: Converting to a Chair structure Draw cis-1-bromo-3-methylcyclohexane as a chair structure. Convert to 3-dimensions – find the positions you need… then determine axial versus equatorial… Down on #1… Down on #3…

  44. Step 3: Converting to a Chair structure Based on MY numbering, you should have had “cis” drawn as two substituents in the DOWN positions, as shown below. The chair structure would look like:

  45. Step 3: Converting to a Chair structure But if you picked a different #1 on the chair, it might look like:

  46. Step 3: Converting to a Chair structure And again: Draw trans-1-chloro-2-ethylcyclohexane as a chair structure. Start in 2-D…. Pick a #1 and number CW or CCW… Add your groups… Give them stereochemistry (wedges/dashes) to show “trans”…

  47. Step 3: Converting to a Chair structure Trans-1-chloro-2-ethylcyclohexane in 2-D….

  48. Step 3: Converting to a Chair structure Keep Going: Draw trans-1-chloro-2-ethylcyclohexane as a chair structure. Remember, there are lots of alternatives, depending on where you placed YOUR #1 and if you went CW or CCW to find #2…

  49. Step 3: Converting to a Chair structure How did you do? Remember that when drawing trans-1-chloro-2-ethylcyclohexane as a chair structure, there are lots of alternatives, depending on where you placed YOUR #1 and if you went CW or CCW to find #2…

  50. Step 4: Drawing a Chair Flip Structure

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