Thus the non-planarity of the cyclohexane ring causes the ring strain to decrease. Thus, it may be expected that the phenomena may be occurring in other smaller ring system to relieve the ring strain (Scheme 13). In fact, the cyclobutane and cyclopropane rings are not planar as well. But, non-planarity alone cannot relieve ring strain because the smaller size of ring does not allow the freedom required to twist the C-C bonds out of plane without cleaving the ring.  The high value of heat of combustion of cyclopropane is a clue to the ring strain due to deviation from the normal bond angle of a sp³ hybridized carbon and also the result of eclipsing of all C-H bonds. In cyclobutane, the ring bends to adopt a so called “puckered ring” shape. This shape though alleviates the eclipsing of C-H bonds but decreases the bond angles to 88.5°, even further to increase the ring strain. Thus, it appears that the eclipsing effect is important. Thus, in cyclopentane, even when the bond angles (108°) are close to the ideal value, there is some strain in the molecule and this causes the cyclopentane to adopt an open envelope form which in turn decreases bond angle and increases angle strain.