Cyclopropane (larger view)

Cyclopropane (larger view)

(How to manipulate JSmol structures)

Cyclopropane

The three carbons of cyclopropane lie in a plane. Indeed, they determine a plane as do any three randomly oriented objects. Three legged stools do not rock! The 27 kcal/mol strain in cyclopropane is due to the eclipsing of all the C-H bonds and the strained C-C-C bond angle. On geometric grounds this angle is 60^o if all C-C bonds were sigma bonds. To relieve some of the strain present in cyclopropane, the C-C bonds rehybridize slightly and cause the C-C-C bond angle to increase. Because the rehybridized bond is no longer symmetrical about the C-C bond axis as would be the case in a normal sp³-sp³ sigma bond, there is more p-character contributed to each C-C bond by each carbon atom. Consequently, each C-H bond has more s-character contributed by carbon. This situation makes the C-H bond shorter and more acidic than the C-H bonds in ethane.