Zh. Chen et Ra. Sachleben, CONFORMATIONAL STUDIES OF SUBSTITUTED DIBENZO-14-CROWN-4 ETHERS - A 1-D AND 2-D H-1 AND C-13 NMR INVESTIGATION, Perkin transactions. 2, (3), 1994, pp. 537-541
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.