outwards so that the inter-orbital angle is 104°.

The unusual structural properties of cyclopropane have spawned many theoretical discussions. One theory invokes ?-aromaticity: the stabilization afforded by delocalization of the six electrons of cyclopropane's three C-C ? bonds to explain why the strain of cyclopropane is "only" 27.6 kcal/mol as compared to cyclobutane (26.2 kcal/mol) with cyclohexane as reference