in surface studies, and benzalacetophenone has been used Infrared spectra are reported of silica preheated at 873 K and as a visual indicator of surface acidity (3). Benzophenones exposed at 295 K to the vapors of four acetophenones (H, 4are not sufficiently volatile for adsorption from the vapor Me, 4-OMe, and 4-NO 2 ). Surface-adsorbate interactions involved phase. However, substituted acetophenones, which have conhydrogen bonding between isolated silanol groups and carbonyl jugate acid pK a values from 04.81 (4-OMe) to 07.94 (4groups, the strength of the hydrogen bonds being related to the NO 2 ), are more volatile and are therefore convenient for electronic effects of the acetophenone ring substituents. The 4study using a variety of oxides which might be expected to OMe compound also generated SiOHrrrOMe hydrogen bonds interact with the indicators in different ways. The present probably via a bridging structure involving two silanol groups study of four acetophenones on silica was aimed at the charperturbed simultaneously by each adsorbed molecule. The mode of adsorption of substituted benzene derivatives on silica is strongly acterization of adsorption behavior primarily involving hydependent on the electronic effects of the substituents on each drogen bonding interactions.
other and on the aromatic p-electron charge density.