title: Influence of the core conformation on the NH-tautomerism in porphyrins: a study of meso-(1,3-dithian-2-yl)porphyrins.
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.
authors.affiliation: Institut für Chemie, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Golm, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Wacker
authors.forename: Katja
authors.initials: K
authors.lastname: Dahms
authors.forename: Mathias O
authors.initials: MO
authors.lastname: Senge
authors.forename: Erich
authors.initials: E
authors.lastname: Kleinpeter
mesh_terms: D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D011166:Porphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D011807:Quinolizines / Q000138:chemical synthesis / Q000737:chemistry; D013457:Sulfur Compounds / Q000138:chemical synthesis / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D011166:Porphyrins; D011807:Quinolizines; D013457:Sulfur Compounds; C438055:dithiane