Uncharged analogues of the phenalenyl cation: Hartree―Fock, Møller―Plesset, and density functional computational investigations of the isomers of boraphenalene

Abstract The four isomers of boraphenalene, 1-bora-, 2-bora-, 3a-bora-, and 9b-boraphenalene, have been examined at the Hartree–Fock 6-31G(d) and the density functional B3LYP/6-31G(d) and B3PW91/6-31G(d) levels of theory as both singlet and triplet species. The Hartree–Fock structures were also examined, and fully optimized, at the Moller–Plesset MP2/6-31G(d) level of theory with all electrons included in the correlation calculations. At the Hartree–Fock level of theory, the ground state systems are the singlet states for 1-bora- and 9b-boraphenalene and the triplet states for 2-bora- and 3a-boraphenalene; the triplet 2-boraphenalene system is the global minimum. Conversely, at both density functional levels of theory, the singlet states are the ground states for all four isomers and the singlet 1-boraphenalene system is the global minimum. At the Moller–Plesset level of theory, the singlet states are the ground states for 1-bora-, 2-bora-, and 9b-boraphenalene, but the triplet state is the ground state for 3a-boraphenalene and the singlet 1-boraphenalene system is the global minimum. The triplet state of the 1-boraphenalene isomer, at the Hartree–Fock and Moller–Plesset levels of theory, is not a minimum, but rather optimizes to a ring-opened triplet system which, when then calculated as a singlet system, transforms to a substituted bora-acenaphthylene.