Cycloalkanes: Structural Variety
Cyclobutane is a non-planar, bent molecule. By deviating from planarity, the eight hydrogen atoms are eclipsed resulting in decreased strain. Part of the molecule is rotated out of the plane by 26°. However, this does not imply that the structure is rigid; it interconverts rapidly from one bent conformation to another. The C-C-C angle of 88.5° still is clearly different from a tetrahedral angle (109.5°) indicating high ring strain.
The dissociation energy of the C-C bond in cyclobutane is very small with a value of 264 . As in cyclopropane, ring opening eliminates the ring strain and allows the formation of new bonds with larger orbital overlap. Though less reactive than cyclopropane, cyclobutane undergoes similar reactions.