The chemistry of pyrrolic compounds. LII. The preferred pathway of electron delocalization in metalloporphyrins

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Measurement of the proton coupling constant in the allylic unit, CH3-C=C-H, of the zinc(II), nickel(II) and magnesium(II) chelates of the deuteroporphyrin isomer (3a) points in each case to the double bond of this system having a significantly diminished bond order. Similar data have been obtained for the dication derivative of (3a). These findings are in accord with the view that the π-electron delocalization pathway in porphyrin dications and metalloporphyrins involves the periphery of the molecule as was previously shown for the metal-free porphyrin. New synthetic approaches to the porphyrin (3a) have been studied.