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

Abstract Each of the isomers of phenalene, 1 H -, 2 H -, 3a H -, and 9b H -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 9b H - and the 1 H -isomer will exist as ground state singlets, the 2 H - and 3a H -phenalenes are predicted to exist as ground state triplets; only the synthesis of the 1 H -isomer has been reported in the literature. Structurally, 1 H - and 2 H -phenalene are planar systems, 3a H - and 9b H -phenalene are non-planar systems puckered at the saturated carbon, and the cation, neutral radical, and anion of phenalenyl are planar D 3h systems.