CHEM 281 Chapter Notes - Chapter 3: Van Der Waals Strain, Cyclohexane, Ring Strain
30 Aug 2018
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Chapter 3 Notes Part 16: An Introduction to Organic Compounds
The chair conformer is so important that you should learn how to draw it:
1. Draw two parallel lines of the same length that slant slightly downward. Start the bottom
line at the midpoint of the top line.
2. Connect the left ends of the parallel lines with a V that points downward; connect the
right end of the parallel lines with a V that points upward. This completes the framework
of the six-membered ring. Your final chair conformer should have three sets of parallel
lines.
3. Each carbon has an axial bond and an equatorial bond. The axial bonds (red lines with red
triangles) are vertical and alternate above and below the ring. The axial bond on one of the
uppermost carbons is up, the next is down, the next is up, and so on
4. The equatorial bonds (red lines with blue balls) point outward from the ring. Because the
bond angles are greater than 90°, the equatorial bonds are on a slant. If the axial bond points
up, then the equatorial bond on the same carbon is on a downward slant. If the axial bond
points down, then the equatorial bond on the same carbon is on an upward slant. Remember
that in this depiction, cyclohexane is viewed edge-on. The lower ring bonds are in front, and the
upper bonds are in back.
Ring Flip
● Cyclohexane rapidly interconverts between two stable chair conformers because of the
ease of rotation about its C-C bonds. This interconversion is called ring flip. (See Figure
3.10 on the next page.)
● When the two chair conformers interconvert, bonds that are equatorial in one chair
conformer become axial in the other chair conformer and bonds that are axial become
equatorial.
Boat Conformer
Document Summary
Chapter 3 notes part 16: an introduction to organic compounds. The chair conformer is so important that you should learn how to draw it: draw two parallel lines of the same length that slant slightly downward. This completes the framework of the six-membered ring. Your final chair conformer should have three sets of parallel lines: each carbon has an axial bond and an equatorial bond. The axial bonds (red lines with red triangles) are vertical and alternate above and below the ring. The axial bond on one of the uppermost carbons is up, the next is down, the next is up, and so on: the equatorial bonds (red lines with blue balls) point outward from the ring. Because the bond angles are greater than 90 , the equatorial bonds are on a slant. If the axial bond points up, then the equatorial bond on the same carbon is on a downward slant.
