cis-1,2-dimethylcyclohexane (2)

You should have come to the conclusion that the two cis-1,2-dimethylcyclohexanes on the previous page are indeed mirror images, and not superimposable. Now, let's try to find out whether they are interconvertible.

Below, in the center, the energy profile of the ring-flip of cis-1,2-dimethylcyclohexane is shown. The starting structure (1) and last structure (34) are also shown.

The animation below the energy profile shows the ring-flip, starting with structure 1 (axial/equatorial) and ending with structure 34 (equatorial/axial). Use the buttons to start/stop the animation.

1 34

Now we ask the same questions as on the previous page: are the structures 1 and 34 mirror images? Are they superimposable?
Confirm that the answers are the same: yes, they are mirror images; and no, they are not superimposable.
And moreover, we show with the animation that they are interconvertible.

Next, compare the two cis-1,2-dimethylcyclohexanes from the previous page
A B

Look at these structures and confirm that:

Since the compounds are chiral, but unresolvable, they will exist as something like a racemic mixture, or 'on average' meso-compounds.

Questions:
  1. Determine the R/S configuration of the chiral centres in 1 or A
  2. Determine the R/S configuration of the chiral centres in 34 or B
  3. Do the structures above represent chiral molecules?
  4. What is the relation between 1 and A?
    And between 1 and B?
  5. Are the mirror images 1 and 34 (or A and B) resolvable enantiomeric structures? Explain.
  6. Enter your name(s):
    and the answers!

On the next page, we will take a look at the relative energies of all the different 1,2-dimethylcyclohexanes. This chapter is concluded with a short quiz.


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