Infrared Study of Substituted Acetophenones Adsorbed on Silica

Abstract

Infrared spectra are reported of silica preheated at 873 K and exposed at 295 K to the vapors of four acetophenones (H, 4-Me, 4-OMe, and 4-NO2). Surface–adsorbate interactions involved hydrogen bonding between isolated silanol groups and carbonyl groups, the strength of the hydrogen bonds being related to the electronic effects of the acetophenone ring substituents. The 4-OMe compound also generated SiOH···OMe hydrogen bonds probably via a bridging structure involving two silanol groups perturbed simultaneously by each adsorbed molecule. The mode of adsorption of substituted benzene derivatives on silica is strongly dependent on the electronic effects of the substituents on each other and on the aromatic π-electron charge density.