The smallest borazine-fused cyclacenes: Novel N–H conformations in cyclo-BN-anthracene and cyclo-BN-tetracene from Hartree-Fock and density functional calculations

Abstract The structures and properties of the smallest possible borazine-fused cyclacenes, cyclo -BN-anthracene and cyclo -BN-tetracene ([6] 3 BN-cyclacene and [6] 4 BN-cyclacene), have been determined at the RHF/6-31G∗ and B3LYP/6-31G(d) levels of theory. In addition, novel conformers of both molecules in which one or more of the N–H moieties are aligned approximately perpendicular to the belt direction have been investigated and have been found to be comparable in energy to the conformers in which all of the N–H moieties are aligned approximately parallel to the belt direction. At the density functional B3LYP/6-31G(d) level of theory, the most stable of these conformers for [6] 3 BN-cyclacene is not the conformer in which all of the N–H moieties are aligned approximately parallel with the belt direction, but rather the conformer in which one of the N–H moieties is aligned approximately perpendicular with the belt direction. For the [6] 4 BN-cyclacene, however, the conformer with all of the N–H moieties aligned parallel to the belt direction is the most stable, although other conformers are reasonably similar in energy.