Crystal and solution structures of 25,27-diethoxycarbonylmethoxy-26,28-dimethoxy-t-butylcalix[4]arene

The crystal and solution structures of diethoxycarbonylmethoxy-26,28-dimethoxy-t-butylcalix[4]arene (2) have been determined. This diester (2) adopts the less common partial cone conformation in the solid state, but in solution, 2 is fluxional at room temperature. Variable temperature 1H NMR spectroscopy shows that at 250 K in CDCl3, 2 exists in a cone and a partial cone in a ratio of 43:57.