Tetraoxa[22]porphyrin(2.2.2.2) Dication and Tetraoxa[24]porphyrinogens(2.2.2.2)

Very flexible and antiaromatic versus relatively rigid and aromatic—that is the difference between [24]porphyrinogen 1 and its oxidation product [22]porphyrin dication 2. Although both compounds occur in the cis, trans, cis, trans configuration, the protons along the inner perimeter of 2 are shifted roughly 20.5 ppm upfield, and the outer protons are shifted approximately 8.4 ppm downfield relative to the corresponding protons in 1.