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  • Title: Influence of the core conformation on the NH-tautomerism in porphyrins: a study of meso-(1,3-dithian-2-yl)porphyrins.
    Author: Wacker P, Dahms K, Senge MO, Kleinpeter E.
    Journal: J Org Chem; 2008 Mar 21; 73(6):2182-90. PubMed ID: 18288865.
    Abstract:
    In order to investigate the mechanism of the NH-tautomerism in porphyrins, three meso-dithianyl-substituted porphyrins of different substitution pattern were studied theoretically. The corresponding trans-, cis- and saddle-point geometries were optimized with DFT methods, and the macrocyclic conformations obtained were analyzed using normal-structure-decomposition (NSD) analysis. Special attention was given to the influence of the participating out-of-plane and in-plane conformations on the NH-tautomerism, and the interplay of substituents, core conformations and energies of the transition-state structures was critically evaluated. The calculated energy barriers of the preferred pathways are compared with experimental activation enthalpies determined by variable-temperature (VT) NMR spectroscopy.
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