Due to the free rotation that is possible around single bonds, different conformations of a molecule are possible. The simplest example of rotation around a single bond which gives rise to different conformations is rotation of the carbon-carbon single bond in ethane. There are two possibilities, staggered and eclipsed. In the eclipsed conformation, hydrogens on adjacent carbons are as close together as possible. In the staggered conformation, they are as far apart as possible. Decide as you watch this movie which conformations would be lower in energy, and which would be higher.

Rotation of the C-C Bond in Ethane (84K)

Same Rotation Shown Down the C-C Bond (81K)

A Slightly more complex example is the rotation observed between the second and third carbons in butane. In the single bond rotation in ethane, a 360 degree rotation resulted in three equivalent staggered conformations and three equivalent eclipsed conformation. Watch the following movies and decide how the different conformations would be ranked with the simple addition of two more carbon atoms.

Rotation of the C2-C3 Bond in Butane (135K)

Same Rotation Shown Down the C2-C3 Bond (120K)

Alkanes containing six-membered rings do not contain these six-membered rings as flat structures. The following movies demonstrate some of the conformational preferences observed for six-membered rings. Note that these movies are not designed to show the lowest-energy path between these conformations (in other words, the mechanism for conformational interconversion). These movies simply show the chair and boat conformations.

Cyclohexane Conformations (504K)

Cyclohexane can adopt conformations name chair and boat. See if you can identify which is which and determine which might be more stable.

Cyclohexane: Axial versus Equatorial Substituents (270K)

A the beginning of this movie, the blue substituents are in the axial positions. What positions are they in at the end of the movie?

Cyclohexane Conformations: t-butyl Substituted (312K)

While watching this movie, ask yourself whether the t-butyl group will have more space in an equatorial or axial position.

Cyclohexane: Comparison of Chair Conformations in t-butyl Substituted (483K)

The two different positions (axial and equatorial) are shown rotating for a better view of the room available to the t-butyl group.