The twist-boat and 'perfect' boat conformation of cyclohexane

The potential energy of the twist boat conformation lies between that of the chair and the half-chair.

View along the C-C bonds, and do some angle measurements.
And, if you are interested: have a look at the symmetry. There is more symmetry than than you might think. Try to locate two C2 axes: one that relates all the red hydrogens with a white one, and another one that maps all H's onto H's with the same colour.


select two atoms to measure distance;
three to measure angle;
or four to measure torsion angle.

What is the reason for the lower energy-content of the twist-boat compared to that of the half-chair? Or, in other words: why is the twist-boat a more stable conformation than the half-chair?
In the twist-boat conformation,

  1. there is more torsional strain and more angle strain
  2. there is less torsional strain and less angle strain
  3. there is more angle strain
  4. there is less angle strain

What is the main reason for the higher energy-content of the twist-boat compared to that of the chair? Or, in other words: why is the twist-boat a less stable conformation than the chair?

In the twist-boat conformation,

  1. there is more torsional strain
  2. there is less torsional strain
  3. there is more angle strain
  4. there is less angle strain

The boat conformation

So far we didn't meet the boat conformation yet. It doesn't appear in the interconversion process that we animated.
Like the half-chair, it is an energy maximum: it is a low lying transition state (much lower than the half-chair!) between two twist-boat structures.


Use these animation control buttons, or click on a red dot in the graph.



Select two atoms to measure distance
Select three, to measure angle
Select four, to measure torsion angle

Note the very low energy barrier. So in fact all the possible chairs, and all twist-boat minima, are connected via these pathways.
Don't get the idea that one chair always moves straight to the 'other' chair: a twist-boat intermediate can move 'sideways' to another twist-boat, and another one, and from there select any other route. The result is a continuously 'wobbling' cyclohexane ring.

A point to philosophize:
Talking about symmetry: what is the symmetry of the boat conformation? If we distinguish between all the atoms (e.g. number them), how many different boat structures can we draw? How many different chairs? How many different twist-boats?

So far for cyclohexane itself. What happens if we introduce substituents?


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