axial and equatorial hydrogens

The animation below shows cyclohexane ring flipping from one chair-conformation to another. These two chairs are of course equivalent and energetically the same.
However, we can detect that an interconversion took place if we look at the substituents, in this case the hydrogens.
We distinguish two sets, coloured red and white.

>>>>rel. energy 0.11 kJ chair conformation<<<<1 rel. energy 1.14 kJ rel. energy 3.76 kJ Select two atoms to measure distance Select three, to measure angle Select four, to measure torsion angle Emphasize the or hydrogens, or

The two sets with different colours are defined as follows:
In one chair conformation, number 1 in the animation above, all the white hydrogen atoms are in what we call axial positions (parallel to the symmetry axis of the ring), while all red hydrogens are equatorial, that is more or less in the plane of the ring.
In the other chair conformation, number 35 in the plot, this is exactly the other way around.

Also notice that the energy barrier is quite low; interconversion will take place rapidly at room temperature.

Energies are from AM1 calculations and are for qualitative discussion only. Better calculations would give different quantitative results. This page was adapted by Bob Hanson for Internet Explorer 4 and Netscape 7 from the original, written by Hens Borkent