Electronic structure of 1,3-diphenyl-2-azaallenyl radical cation

Quantum chemical simulations were conducted to elucidate the electronic structure of the 2-azaallenyl radical cation, a key intermediate in several [3 + 2]-cycloadditions initiated by the oxidation of 2H-azirine. We propose one additional Lewis structure in resonance with the commonly accepted two Lewis structures for the model system of 1,3-diphenyl-2-azaallenyl radical cation, drawn from comprehensive theoretical data including molecular shape, bond order analysis, partial atomic charges, and spin densities. In addition to the ground state chemistry, the chemical structure of excited state species can be also understood with these three Lewis structures. Theoretical data imply that a newly suggested one mainly accounts for the ground state structure, and the excited state structure is better represented by the previously reported ones. Our claim is further bolstered by the prediction of the excited state geometries of the dicationic and neutral species. This research presents the extended set of Lewis structures for a better understanding electronic structure of 2-azaallenyl radical cation.