The isomers of phenalene and their singlet and triplet states: A Hartree–Fock and density functional computational investigation

Each of the isomers of phenalene, 1H-, 2H-, 3aH-, and 9bH-phenalene, as well as the cation, neutral radical, and anion in the phenalenyl system, have been examined at the Hartree–Fock 6-31G(d) and the density functional B3LYP/6-31G(d) levels of theory. The structures and properties of the phenalenes were determined as both singlets and triplets. While the data indicate that both the 9bH- and the 1H-isomer will exist as ground state singlets, the 2H- and 3aH-phenalenes are predicted to exist as ground state triplets; only the synthesis of the 1H-isomer has been reported in the literature. Structurally, 1H- and 2H-phenalene are planar systems, 3aH- and 9bH-phenalene are non-planar systems puckered at the saturated carbon, and the cation, neutral radical, and anion of phenalenyl are planar D_3h systems.