October 31 - Cycloalkanes

Question 1

Angle strain

Answer 1

Deviation from 109.5° bond angle which causes strain

Question 2

Chair conformer

Answer 2

Six-membered rings that are almost completely free of strain, they have a bond angle of 109.5°

Question 3

How to draw a chair conformer

Answer 3

1. Draw two parallel lines slanted upward
2. Connect top lines with a v, left side slightly longer than right. Connect bottom lines with inverted v
3. Draw vertical axial bonds going up on the uppermost carbons on the rings and going down on the lowermost carbons
4. Draw equatorial bonds (lines with ball at tip) pointing outward from the ring. They have a downward slant when next to a vertical axial bond going up, and an upward slant when next to an axial bond going down

Inverted v for step 2 is equal length both sides

In this depiction, the lower bonds of the ring are in front and the upper bonds are in the back

Question 4

1,3 diaxial interactions

Which conformer will be more common as a result of these 1,3 diaxial interactions, the ones with a substituent in an equatorial or axial position?

Answer 4

When axial substituents are in 1,3 positions relative to each other it leads to unfavorable steric interactions, so the equatorial conformer is more common

This means that at any time

Question 5

Tips for cyclohexane chairs

Answer 5

The larger the group, the more it prefers the equatorial position for stability

Question 6

Fused cyclohexane rings

Answer 6

Trans fused rings are more stable than cis fused rings

Question 7

Ring flip

Answer 7

Carbons are moved over by one
Equatorial switches to axial and vice versa