Examine the conformation of cyclohexane

•	Display the structure of cyclohexane by clicking on the refcode CYCHEX from the Structure Navigator on the right hand side of the main Mercury window.

•	From our analysis of crystal structure data we have determined that six-membered rings are essentially free of angle strain. Inspect the structure of cyclohexane and explain why this is.

•	Cyclohexane adopts a puckered conformation that relieves all strain. This conformation is called the chair.

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In the chair conformation of cyclohexane all bond angles are close to the ideal tetrahedral angle of 109.5 degrees. In addition, viewing along any of the C-C bonds clearly shows that there are no eclipsing C-H interactions. All bonds are fully staggered, i.e. in a gauche arrangement, giving the lowest possible energy. This is why cyclohexane is essentially strain-free.

•	In the vast majority of compounds containing a cyclohexane ring, the molecule exist almost entirely in the chair form. However, other cyclohexane conformations are know. These conformations and substituted cyclohexanes are dealt in detail elsewhere (CSD teaching module #n).

 

 

Chair conformation of cyclohexane (CYCHEX)