DFT calculations of pentalenoquinones: towards the interception of 2-bromopentalene-1,5-dione

To reveal the stability and the aromatic character of pentalenoquinones (PQs) 1-4 and the corresponding bromo derivatives (Br-PQs) 6-9, DFT calculations (B3LYP/6-311+G(d,p)) concerning the geometry optimization, total energy and nucleus independent chemical shift (NICS) values were performed. It was found that all of the compounds have planar geometry. As the energy difference between HOMO-LUMO energy levels (Delta epsilon=epsilon(LUMO) - epsilon(HOMO)) and total energies were considered for the pentalene family, the stability order was found to be 1 > 2 > 3 > 4 for PQs, and 6 > 7 > 8 > 9 for Br-PQs. Furthermore 2-bromopentalene-1,5-dione (6) in solution was investigated and noted that it was too reactive to be isolated or even trapped.