The NMR Spectra of the Porphyrins. 16-Zinc(II) meso-Tetraphenylporphyrin (Zn TPP) as a Diamagnetic Shift Reagent. A Quantitative Ring Current Model

Article abstract of DOI:10.1002/mrc.1270140519

The facile preparation of zinc(II) meso-tetraphenylporphyrin (Zn TPP) and derivatives from substituted benzaldehydes and pyrrole, combined with the calculation of ring current shifts in these molecules, provides a useful series of selective diamagnetic shift reagents.The porphyrin-ligand equilibrium is examined for some nitrogenous bases and the complexation shifts (ΔP values) are obtained in precisely the same manner as LIS.The parameterization of the double-dipole model of the porphyrin ring current is given, with the inclusion of the phenyl ring currents and free rotation about the substrate-Zn bond.Precise agreement with the porphyrin proton chemical shifts and the complexation shifts of the geometrically rigid substrates of pyridine, 4-picoline and quinuclidine is obtained.In contrast, the 13C complexation shifts in these molecules are subject to additional effects other than the ring current shift.