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NMR study of thermodynamic and structural properties of molecular complexes formed by metalloporphyrins and aromatic substrates
Author(s) -
Kitaigorodski Alexander N.,
Edlund Ulf
Publication year - 1991
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260290711
Subject(s) - chemistry , chemical shift , porphyrin , pyridine , chemical stability , naphthalene , bicyclic molecule , cobalt , benzene , molecule , aromaticity , proton nmr , adduct , crystallography , spin–lattice relaxation , relaxation (psychology) , paramagnetism , computational chemistry , stereochemistry , photochemistry , inorganic chemistry , organic chemistry , social psychology , psychology , physics , quantum mechanics
1 H NMR shifts and 13 C spin–lattice relaxation rates were measured for various aromatic π‐acceptors (S) in solutions containing paramagnetic cobalt(II) and iron(III) porphyrins (P). The stability constants of P · S molecular complexes and limiting values of substrate chemical shifts in the complexes were determined from the concentration dependence of chemical shifts. The abilities of different substituents to promote complexation of aromatics with metalloporphyrins are discussed. The preferred substrate orientation in molecular complexes were derived using relative values of chemical shifts and relaxation rates induced by metalloporphyrins. Both monocyclic (benzene and pyridine derivatives) and bicyclic (naphthalene derivative) substrates tend to form ‘axially symmetric’ adducts with parallel π‐planes and the centre of the aromatic system situated in the vicinity of the porphyrin z ‐axis.