text: It was long considered that the best examples of neutral homoaromatics are bishomoaromatics such as barrelene and semibullvalene. First synthesized in 1966, semibullvalene has a structure that should lend itself well to homoaromaticity although there has been much debate whether semibullvalene derivatives can provide a true delocalized, ground state neutral homoaromatic compound or not. In an effort to further stabilize the delocalized transition structure by substituting semibullvalene with electron donating and accepting groups, it has been found that the activation barrier to this rearrangement can be lowered, but not eliminated. However, with the introduction of ring strain into the molecule, aimed at destabilizing the localized ground state structure's through the strategic addition of cyclic annulations, a delocalized homoaromatic ground-state structure can indeed be achieved.
  Of the neutral homoaromatics, the compounds best believed to exhibit neutral homoaromaticity are boron containing compounds of 1,2-diboretane and its derivatives. Substituted diboretanes are shown to have a much greater stabilization in the delocalized state over the localized one, giving strong indications of homoaromaticity. When electron-donating groups are attached to the two boron atoms, the compound favors a classical model with localized bonds. Homoaromatic character is best seen when electron-withdrawing groups are bonded to the boron atoms, causing the compound to adopt a nonclassical, delocalized structure.