Aza Crown Ethers. 13C and 1H NMR Studies of Ring Conformations and Stereochemically Dependent Shifts in N-Substituted Dibenzodiaza-18-crown-6 Ethers and a Nine-Membered Analog

Article abstract of DOI:10.1002/mrc.1260290206

Remarkably large (>10 ppm) 13C NMR chemical shift differences are observed in solution and in the solid phase between ortho aromatic carbons of structurally dibenzodiaza-18-crown-6 ethers and their 9-membered ring counterparts.On the basis of geometries deduced from 1H1H NOESY results, the upfield 13C chemical shifts in the 18-membered systems are attributed to cis coplanar interactions between the terminal carbons of these torsional networks.Overall mobilities of 9- and 18-membered ring systems are examined via 13C spin-lattice relaxation times.