Examine the conformation of cyclopropane

•	Display the structure of cyclopropane by typing QQQCIS01 in the Entry box above the structure list on the left hand side of the WebCSD page.

•	Examine the structure. The three carbon atoms of cyclopropane lie in a plane. Three membered rings must be planar since it is always possible to draw a plane through any three points.

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We know already that there is considerable angle strain in this planar molecule. This is due to the bond angles deviating from the ideal tetrahedral value of 109.5 degrees. However, there is a further cause of strain in cyclopropane. Can you identify what this is? (hint: it may help to view along one of the C-C bonds).

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All the C-H bonds in cyclopropane are eclipsed. This is energetically unfavourable and any rotation would lead to a more stable conformation. however, C-C bond rotation is impossible and so all the C-H bonds are forced to eclipse their neighbours. The strain resulting from eclipsed conformations is called Pitzer strain.