Several calix[4]arenediquinones 3a-e having quinone moieties in opposite positions (diametrical) have been synthesized by oxidation of 25,27-dialkoxycalix[4]arenes 2a-e with Tl(NO3)3 · 3H2O in organic solvents. The conformationalproperties of these compounds have been established in the solid state by X-ray crystallography and in solution by variable-temperature dynamic NMR. We found that the calix[4]arenediquinones