Remarkably large (> 10 ppm) 13C NMR chemical shift differences are observed in solution and in the solid phase between ortho aromatic carbons of structurally analogous 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. Copyright

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Keywords 13C NMR, 1H NMR, Chemical shifts, Conformation, N‐Substituted dibenzodiaza‐18‐crown‐6 ethers, Stereochemistry
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Journal Magnetic Resonance in Chemistry
Buchanan, G.W, & Landry, D.J. (1991). 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. Magnetic Resonance in Chemistry, 29(2), 127–132. doi:10.1002/mrc.1260290206