Conformational studies of substituted dibenzo-14-crown-4 ethers: a 1-D and 2-D 1H and 13C NMR investigation

Abstract

The solution structures of substituted dibenzo-14-crown-4 ethers have been investigated by one- and two-dimensional NMR methods (proton vicinal coupling constants, ¹³C 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) linking the substituent to the crown ring. Substituents attached by a carbon linkage, including methyl, 2-hydroxyethyl and carboxymethyl, prefer a pseudo-equatorial conformation, i.e. with the substitutent oriented anti to the ring C–O bond. Substituents attached by an oxygen linkage, including hydroxy, methoxy, and carboxymethoxy, prefer the pseudo-axial (gauche) conformation.