{{Short description|Chemical structure derived from cyclopropane}} thumb|right|upright|Chemical structure of the cyclopropyl group
A '''cyclopropyl group''' is a chemical structure derived from cyclopropane; it is typically produced in a cyclopropanation reaction. The group has an empirical formula of C<sub>3</sub>H<sub>5</sub> and chemical bonds from each of the three carbons to both of the other two.
== Structure and bonding == 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<sup>~5</sup>-hybrids for the ring bonds and sp<sup>~2</sup> 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<sup>2</sup>-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 cation's HOMO isolobal to the allyl anion's HOMO.<ref>{{Cite journal|last1=Jung|first1=Sebastian T.|last2=Nickisch|first2=Roman|last3=Reinsperger|first3=Tony|last4=Luy|first4=Burkhard|last5=Podlech|first5=Joachim|date=April 2021|title=Stereoelectronic effects: Perlin effects in cyclohexane‐derived compounds|journal=Journal of Physical Organic Chemistry|language=en|volume=34|issue=4|doi=10.1002/poc.4165|s2cid=229407105 |doi-access=free}}</ref>
== Literature == * Zvi Rappoport (Ed.), The Chemistry of the Cyclopropyl Group, Band 1, Wiley, Chichester u. a. O., 1987. Vol 2, Wiley, Chichester 1995, ISBN 0-471-94074-7.
== References == {{Reflist}} {{Commonscat}} Category:Functional groups Category:Cyclopropyl compounds