How Should Aromaticity Be Described in Porphyrinoids?

摘要

Modern porphyrinoid chemistry has benefited particularly strongly from Huckels simple description of aromaticity, which explains the formation of stable aromatic compounds by the presence of 4n+2 cyclic conjugated it electrons. In the early 1930s porphyrins were already discussed as possible aromatic systems with aligned C—C bonds. However, since the Huckel theory does not apply to polycyclic systems, it required the development and application of new analytical techniques, including single-crystal diffraction and NMR spectroscopy, to enforce this point of view. In particular, the similarity of the physical data obtained for 1 by these methods with those of the [18]annulene 2 reported by Sondheimers et al. in 1962 led to the general acceptance of the interpretation of porphyrin as a multiple-bridged aromatic diaza[18]annulene system.