Cyclopropenyl free radical

In the allyl system (Fig. 29.7) the third and fourth electrons go into a non-bonding orbital, whereas here they go into antibonding orbitals. As a result, the cyclopropenyl free radical and anion are less stable than their open-chain counterparts. For the cyclo-propeny] anion in particular, with two electrons in antibonding orbitals, simple calculations indicate no net stabilization due to delocalization, that is, zero resonance energy. Some calculations indicate that the molecule is actually less stable than if there were no conjugation at all. Such cyclic molecules, in which delocalization actually leads to destabilization, are not just non-aromatic they are u/i/iaromatic. 

Figure 29.11. Cyclopropenyl system. Configuration of n electrons in cation, free radical, and anion.

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