Pressure-induced condensation of organic anhydrides

Carbonyl–carbonyl (CC) interactions are emerging noncovalent interactions found in many small and macro molecules. They are of quantum-mechanical nature, where overlap of n and π* wavefunctions occurs along the trajectory which ensures the maximum orbital overlay. In some of the organic anhydride (OA) crystals, the intermolecular CC contacts along this trajectory are exceptionally short and direct the molecules for the nucleophilic addition reaction . We recently discovered a crystal structure distortion and dramatic change in C=O vibrational modes in pyromellitic dianhydride at high pressure. We associate it with intra-crystal polymerization, as a result of an effective overlap of C=O groups. In this proposal, we aim to systematically study a series of simple maleic anhydride derivatives, using high-pressure X-ray diffraction technique, in order to derive general rules for pressure-driven condensation in OA crystals, depending on their electronic and supramolecular structure.