As might be expected, calculations have demonstrated that the HOMO is composed of the nonbonding electrons on boron (nσ-type, sp character). The LUMO and LUMO+1 are empty, orthogonal pπ-type orbitals and are degenerate in energy except in the case where R breaks the symmetry of the molecule, thus lifting the degeneracy. Unlike carbenes, which can exist in either singlet or triplet ground states, calculations have indicated that all yet-studied borylenes have a singlet ground spin state. The smallest singlet-triplet gap was calculated to be 8.2 kcal/mol for Me3Si-B. Aminoborylene (H2NB) is a slight exception to the above paradigm, as the nitrogen lone pair donates into an unoccupied boron p orbital. Thus, there is formally a double bond between boron and nitrogen; the π* combination of this interaction serves as the LUMO+1.
