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.

Background >>>>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.

As a first excercise, try to confirm this statement by examining the structure, looking at the animation by stepping through it. You can rotate the structure using the left mouse button.
Use the navigation buttons, or click on the points in the graph, to display particular conformations.
We will focus on the maxima and minima in the next exercises.
Also notice that the energy barrier is quite low; interconversion will take place rapidly at room temperature.

This page was adapted by Bob Hanson for Internet Explorer and Netscape 7 from our original.