Aromaticity and Tautomerism in Porphyrins and Porphyrinoids

Abstract

Porphyrins and their analogues constitute one of the most important families of aromatic macrocycles. The present review discusses aromaticity of porphyrinoids, focusing mainly on non-expanded systems. The effect of structural modifications on the aromaticity-dependent properties of porphyrin-like macro- cycles is described. It is shown that delocalization modes observed in porphyrinoids can be classified using a simple valence-bond approach. Aromaticity of porphyri- noids is further discussed as a function of tautomerism, coordination chemistry, and the oxidation state of the macrocycle.