Conformations of Cyclohexane

 Conformations of Cyclohexane

1) Rings larger than cyclopentane would have angle strain if they were planar. However, this strain, together with the eclipsing strain inherent in a planar structure, can be relieved by puckering the ring. 

2) Cyclohexane is a good example of a carbocyclic system that virtually eliminates eclipsing and angle strain by adopting non-planar conformations.

3)  Cycloheptane and cyclooctane have greater strain than cyclohexane, in large part due to transannular crowding (steric hindrance by groups on opposite sides of the ring).

4) Cyclohexane is rapidly rotating between the two most stable conformations known as the chair conformations in what is called the "Chair Flip" shown below.

chair flip.png

5) Several other notable cyclohexane conformations occur during the transition from one chair conformer to the other- the boat, the twist, and the half-chair. 
 6) The relative energies of the conformations is a direct reflection of their relative stabilities. 

* Energy order:

                Half chair >  boat > Twist boat > chair form

* Stability order  of cyclohexane conformations:

                Half chair < boat < Twist boat < chair form

    These structural and energetic relationships are summarized in the conformational energy diagram for cyclohexane below.


 

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