1. 3.9 Small Rings
Cyclopropane
Cyclobutane 25

2. Cyclopropane
sources of strain
torsional strain
angle strain 26

3. nonplanar conformation relieves some torsional strain
Cyclobutane
nonplanar conformation relieves some torsional strain
angle strain present 27

4. 3.10 Cyclopentane 28

5. all bonds are eclipsed in planar conformation
Cyclopentane
all bonds are eclipsed in planar conformation
planar conformation destabilized by torsional strain 29

6. Nonplanar Conformations of Cyclopentane
Envelope
Half-chair
Relieve some, but not all, of the torsional strain.
Envelope and half-chair are of similar stability and interconvert rapidly. 30

7. 3.11 Medium and Large Rings 28

8. Cycloheptane and Larger Rings
More complicated than cyclohexane.
Common for several conformations to be of similar energy.
Principles are the same, however. Minimize total strain. 26