Mostly made up from the p-orbital on the carbonyl oxygen atom. | 
Mainly the p-orbtail on the sp2 carbon, in anti-bonding combination with the parallel p-orbitals on the neighbouring O atoms (pi*-like) |
| | HOMO | LUMO |
| C1 2s | 0.055974 | -0.000000 |
| C1 2px | 0.000000 | -0.098378 |
| C1 2py | -0.019863 | 0.000000 |
| C1 2pz | 0.275212 | -0.000000 |
| C2 2s | 0.064969 | 0.000000 |
| C2 2px | 0.000000 | -0.769115 |
| C2 2pz | -0.117175 | 0.000000 |
| O3 2s | 0.000845 | -0.000000 |
| O3 2px | 0.000000 | 0.537090 |
| O3 2py | 0.496910 | -0.000000 |
| O3 2pz | 0.722066 | 0.000000 |
| O4 2s | -0.019277 | -0.000000 |
| O4 2px | 0.000000 | 0.248279 |
| O4 2py | 0.345622 | -0.000000 |
| O4 2pz | 0.004129 | 0.000000 |
| H5 1s | 0.049632 | 0.000000 |
| H6 1s | -0.088390 | -0.000000 |
| H7 1s | -0.046462 | 0.156007 |
| H8 1s | -0.046462 | -0.156007 |
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