The recently proved one-to-one structural equivalence between a conjugated hydrocarbon CnHm and the corresponding borane BnHm+n is applied here to hybrid systems, where each C=C double bond in the hydrocarbon is consecutively substituted by planar B(H2)B moieties from diborane(6). Quantum chemical computations with the B3LYP/cc-pVTZ method show that the structural equivalences are maintained along the substitutions, even for non-planar systems. We use as benchmark aromatic and antiaromatic (poly)cyclic conjugated hydrocarbons: cyclobutadiene, benzene, cyclooctatetraene, pentalene, benzocyclobutadiene, naphthalene and azulene. The transformation of these conjugated hydrocarbons to the corresponding boranes is analyzed from the viewpoint of geometry and electronic structure.
Keywords: boron; conjugated hydrocarbon; electronic structure; isoelectronic molecule; quantum chemistry; singlet-triplet gap.