Chemistry - GOC Question with Solution | TestHub

The $\mathrm{C}=\mathrm{O}$ group is polarised (C+ O-). In cyclopropenone the ring in this resonance form is the cyclopropenyl cation (2 π electrons, aromatic). In cyclopentadienone it is the cyclopentadienyl cation (4 π electrons, anti-aromatic), so the molecule is very reactive and cannot be isolated.