The effect of induced aromaticity on sorption of organic molecules by montmorillonite: Comparison of dibenzosuberone with dibenzotropone

Despite the close resemblance of the molecular structures of the two title compounds, major differences were found in their adsorption characteristics on Na, Cu, Mg, Ni, Fe, and Al montmorillonite. These differences are reflected in electronic and infrared (IR) spectra, in orientational IR spectra, in basal spacings determined by X-ray diffraction, and in their rate of adsorption as determined by chemical analysis. Generally it is found that the interaction of dibenzotropone (DBT) with the clay surface is much stronger than that of dibenzosuberone (DBS). The differences in the adsorption characteristics of the two compounds are attributed to induction of tropylium aromaticity which can occur in DBT but not in DBS. Both hydrogen-bond interactions with the acidic interlayer water molecules and interactions of the planar positively charged aromatic moiety in DBT are responsible for the unusually strong DBT-clay interactions. These are weaker in DBS. All the analytical data support this adsorption mechanism and corroborate the theoretical predictions that (4n + 2) π electron aromaticity can be induced in DBT but not in DBS.