CONFORMATIONAL STUDIES OF SUBSTITUTED DIBENZO-14-CROWN-4 ETHERS - A 1-D AND 2-D H-1 AND C-13 NMR INVESTIGATION

The solution structures of substituted dibenzo-14-crown-4 ethers have been investigated by one- and two-dimensional NMR methods (proton vici nal coupling constants, C-13 chemical shifts and ROESY). The preferred conformations in solution for substituents on sym-dibenzo-14-crown-4 ethers have been shown to depend on the atom (carbon or oxygen) linkin g the substituent to the crown ring. Substituents attached by a carbon linkage, including methyl. 2-hydroxyethyl and carboxymethyl, prefer a pseudo-equatorial conformation, ie. with the substitutent oriented an ti to the ring C-O bond. Substituents attached by an oxygen linkage, i ncluding hydroxy, methoxy, and carboxymethoxy, prefer the pseudo-axial (gauche) conformation.