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Investigation of the Tautomerism of 15 N‐Labeled Hydroporphyrins by Dynamic NMR Spectroscopy
Author(s) -
Schlabach Martin,
Rumpel Helmut,
Limbach HansHeinrich
Publication year - 1989
Publication title -
angewandte chemie international edition in english
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 0570-0833
DOI - 10.1002/anie.198900761
Subject(s) - tautomer , pyrrole , porphyrin , intramolecular force , chemistry , ring (chemistry) , proton , photochemistry , proton nmr , spectroscopy , nuclear magnetic resonance spectroscopy , chlorin , crystallography , stereochemistry , organic chemistry , physics , quantum mechanics
The barrier height for tautomerism of the inner protons of porphyrin is significantly influenced by specific reduction of the pyrrole rings. In the tetraphenyl derivatives of chlorin and bacteriochlorin an aromatic ring current was established 1 H NMR spectroscopically; in contrast, in the tetraphenyl derivative of isobacteriochlorin it is virtually absent. The activation barrier in the hydrogenation of a pyrrole ring is ca. 20 kJ mol −1 higher. In the hydrogenation of two adjacent rings a system is formed in which two symmetric double minimum potentials of differing barrier height have been demonstrated for the first time for an intramolecular proton transfer.