Cyclobutane

Cyclopentane Envelope

Cyclpentane Twist

Cyclobutane is not static; it flaps its "wings"; that is, it folds back and forth along the diagonal.

Cyclopentane exists as a mixture of the two conformers, which have about the same energy. Each one undergoes a process called pseudorotation, in which each atom takes a turn in the out of plane positions.. For the envelope, for example, this give the appearance of the molecule rapidly spinning about an axis through the middle of the ring.

Cycloheptane

Cyclooctane

Cycloheptane exists in four conformations, of which the most stable, called the twist-chair, is shown. The others range from 1-3 kcal/mol less stable, and are appreciably populaated at room temperature.

As many as 11 conformations have been suggested for cyclooctane, all within about 8 kcal/mol of each other. The most stable one is shown, the boat-chair.

As ring size goes up the molecules become much "floppier" and more like a collection of long chains, with a multitude of gauche-like conformations of very similar energies.