RING STRAIN-ENERGY AND INVERSION BARRIER OF PHOSPHA[3]RADIALENE AND AZA[3]RADIALENE

The geometries of [3]radialene, aza[3]radialene, and phospha[3]radialene were completely optimized at the HF/6-31G* level. The ring strain energies of these species were evaluated using group equivalent reactions and found to be 52.86, 49.96, and 35.84 kcal mol-1, respectively. The heteroatomic radialenes both have nonplanar heteroatoms. The inversion barriers (at MP2/6-31G*) for aza[3]radialene and phospha[3]radialene are 7.96 and 54.10 kcal mol-1, respectively. The geometries, ring strain energies, and inversion barriers are discussed in terms of relative electron delocalization between the exocyclic pi-bonds and the lone pair.