Cyclopropanone is the prototype molecule exhibiting pseudo aromaticity. The dominant resonance form is shown in Scheme 2. We demonstrate how the electronic structure affects the geometries of 1, 2, and cyclopropanone, 3. All three of these structures are shown in Figure . We first compare the 𝜋 CO bonds in 1-S0, 2-S0, 3-S0 three structures, which are 1.20 or 1.21 Å. In pseudo aromatic structures 1-S0 and 2-S0 the σ CC bonds are 1.44 Å in 1-S0 and 2-S0 and 1.47 Å in non-aromatic 3-S0. The relatively short σ CC bonds in 1-S0 and 2-S0 suggest that the 𝜋 CC is conjugated with 𝜋 CO . Next, we computed the excitation energies and electronic transitions of 1 and 2 with time-dependent density functional theory (TD-DFT) and multiconfigurational complete active space self-consistent field (CASSCF). We extended multi-state complete active space second-order perturbation theory (XMS-CASPT2). Our TD-DFT calculations included the lowest 10 singlet excited states and used the range-separated density functional CAM-B3LYP-D3BJ with the triple-ζ aug-cc-pVTZ basis set. We included 10 electrons and 9 orbitals in the CASSCF active space for 1 and 2 as shown in Figure , along with their average orbital occupancies. The excitations, oscillator strengths, and transition natures for 1 and 2 were computed at the SA(4)-CASSCF(10,9)/ANO-VDZP, SA(4)-XMS-CASPT2(10,9)/ANO-S-VDZP, and TD-DFT levels of theory (Table and).