Shortened CC Bonds and Antiplanar OCOH Torsion Angles in 1,4‐Cubanedicarboxylic Acid

Larger bond angles—shorter bond lengths: This interrelationship gained further confirmation by the X‐ray structure analysis of 1,4‐cubanedicarboxylic acid. Whereas the exocyclic CC bonds (bond angle ca. 125°) are shortened to about 1.48 Å, the endocyclic CC bonds are stretched to about 1.57 Å. Moreover, the antiplanar OCOH partial conformation found in half of the molecule, which could be favored by the layer‐packing of the cubanedicarboxylic acid molecules, is very rare.