Due to the unfavoured bond angles (60°), cyclopropyl groups are highly strained. Two orbital models were proposed to describe the bonding situation. The Coulson-Moffit model uses bent bonds. The C-C bonds are formed by overlap of two sp-hybrid orbitals. To adapt to the small bond angle, there is some rehybridization resulting in sp-hybrids for the ring bonds and sp for the C-H bonds. This model resembles the banana bond model for C=C double bonds (τ bonds).
Alternatively the structure can be explained with the Walsh model. Here the two sp-hybrids forming the ring bond are separated into one sp-hybrid and one pure p-orbital. This corresponds to the π bond description of C=C double bonds.
Cyclopropyl groups are good donors in hyperconjugation resulting in a considerable stabilization of carbocations. In contrast to double bonds, stabilization of radicals is weaker and stabilization of carbanions is negligible. This is explained by the occupation of the π system with two more electrons, making the cyclopropyl methyl cations HOMO isolobal to the allyl anions HOMO.