Electronic Structure and Stability of Ethenedione

The stmcture 1 is somewhat misleading, in that taken literally it implies a closed-shell molecule with the orbital pattern 

hemaxs. Modeling Marvels, DOI 10.1007/978-l-4020-6973 9, Springer Science+Business Media B.V. 2008 

However, theoietical considerations indicate that the oibitals are arrayed energetically so that the two uppermost elections must be placed in degenerate tt molecular orbitals [19]  

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