Conformational Effects on the Redox Potentials of Tetraarylporphyrins Halogenated at the β‐Pyrrole Positions

Despite four additional electron-withdrawing substituents, the octahalogenated porphyrins 2 are more easily oxidized than their tetra-halogenated counterparts 1. This apparent paradox can be explained by the structures of the molecules: porphyrins 2 are almost planar, whereas in 1 steric interactions are minimized by a saddle conformation, which makes these porphyrins easier to oxidize.