Ab initio calculations of all-trans octatetraene and eigh isoelectronic conjugated chains: semiempirical heats of formation and stabilization energies

In the framework of our study of the changes of the electric polarizability upon substituting heteroatomic linkages in conjugated hydrocarbon backbones, we have been led to examine the relative stability of eight compounds isoelectronic to the all-trans octatetraene using the Cox and Pilcher concept of stabilization energy (SE), SE = ΔHa – ΣNABEAB, where ΔHa is the heat of atomization of the species under consideration and the EAB's are bond-energy terms. Full geometry optimizations at the 4-31G level have been performed to obtain the equilibrium geometries needed to deduce reliable semiempirical heats of formation from appropriate isodesmic processes. Some of the compounds containing the  CHN and  NN  groups have electric polarizabilities and stabilization energies comparable to octatetrene.