MOLECULAR-ORBITAL STUDY OF THE CLEAVAGE OF ASPIRIN CRYSTALS

It is well known empirically that aspirin crystals have a cleavage plane. The cleavage of aspirin crystals was studied from a quantum chemical point of view by using the CNDO/2 and ab initio methods. In the aspirin crystals the dimer with two hydrogen bonds through two carboxyl groups was more stable in comparison with any other dimers without hydrogen bonds. The interaction energy of the hydrogen bonded dimer was due to charge transfer and electrostatic interaction terms. In order to clarify the intermolecular interaction energies in the cleavage plane, interaction energies in four planes of aspirin crystals were calculated. As the results it was shown that the intermolecular interaction energy in the cleavage plane was smallest. © 1979 American Chemical Society.