NMR studies on the Li+ and Na+ complexes of dibenzo-14-crown-4 lariat ethers

Abstract

The Li⁺ and Na⁺ complexes of a series of substituted dibenzo-14-crown-4 ethers bearing alkyl, ether, hydroxylic and carboxylic functional groups have been investigated in solution by ¹H and ¹³C NMR spectroscopy. As was found previously for the uncomplexed ligands, the orientation of the sidearm relative to the crown cavity in the complexes depends on the nature of the atom linking the sidearm to the macrocyclic ring. Most significantly, when the sidearm is attached to the macrocyclic ring through an ether linkage the sidearm is oriented towards the cavity, resulting in intramolecular interactions between the bound carbon and secondary donor groups on the sidearm, which appear to be stronger for sodium than for lithium.