Conformational analysis by chemical shift simulation: structure of 1,4,11,14-tetraoxa[4.4]metacyclophane

Conformational analysis of 1,4,11,14-tetraoxa[4.4]metacyclophane was carried out using a combination of the molecular mechanics calculation, analysis of the temperature dependent 1H NMR signal change and the chemical shift simulation method. The molecular mechanics calculation with Amber* force-field gave the two structures, one is highly symmetric C2v and the other is Ci symmetric. The latter is identical to the structure found in the crystal. Both of the structures were confirmed by the chemical shift simulation.