If you were to join six tetrahedral carbon atoms together, you would probably find that you ended up with a shape like this.

All the carbon atoms are certainly not in the same plane, and there is no strain because all the bond angles are 109.5°. If you squash the model against the desk, forcing the atoms to lie in the same plane, it springs back into this shape as soon as you let go. If you view the model from one side (the second picture above) you will notice that four carbon atoms lie in the same plane, with the fifth above the plane and the sixth below it (although it’s important to realize that all six are identical—you can check this by rotating your model). The slightly overly imaginative name for this conformation—the chair conformation—derives from this view.

There is another conformation of cyclohexane that you might have made that looks like this.

This conformation is known as the boat conformation. In this conformation there are still four carbon atoms in one plane, but the other two are both above this plane. Now all the car bon atoms are not the same—the four in the plane are different from the ones above. However, this is not a stable conformation of cyclohexane, even though there is no bond angle strain (all the angles are 109.5°). In order to understand why not, we must go back a few steps and answer our other question: why is cyclopentane strained even though a planar conformation has virtually no angle strain?

مواضيع ذات صلة

E1 reactions can be stereoselective

The role of the leaving group

Substrate structure may allow E1

E1 and E2 mechanisms

Size

Elimination happens when the nucleophile attacks hydrogen instead of carbon

Axially and equatorially substituted rings react differently

Steroid

Decalins

What happens with more than one substituent on the ring

Substituted cyclohexanes

The ring inversion (flipping) of cyclohexane