Macrocyclic tetralactams : Structural behaviour of three 21-membered rings and their Ca2+ complexes as evidenced by13C and19F NMR

Article abstract of DOI:10.1016/S0040-4039(00)92120-8

a stepwise synthesis of three macrocyclic tetralactams selective complexants of Ca²⁺ vs. alkali and Mg²⁺ ions is reported. The multiplicity of the resonances in ¹³C and ¹⁹F n.m.r. spectroscopy is related to the restricted rotations around the carbon-nitrogen bond of the four amide moieties. The 1/1 complexes formed by addition of one equivalent of Ca(ClO₄)₂ exhibit very simple spectra which are assigned to the existence of a single form in the complex with the carbonyl oxygen atoms in the same orientation.