Hückel's rule
According to Hückel's rule which states that a cyclic molecule is aromatic if it has π electrons and antiaromatic if there are electrons, boroles represent antiaromatic molecules. In agreement with chemical intuition, "ab initio" calculations on the parent borole predict it to have an antiaromatic singlet ground state. Its backbone structure features strongly alternating bond lengths, consistent with localised electrons in the π system. This characteristic is preserved in almost all structurally characterised borole derivatives except those derived from . This discrepancy was attributed to intermolecular phenyl→boron π donation within dimeric subunits.