Carbon-13 NMR and infrared spectroscopic investigations of acetone adsorbed on silica gel surfaces

Abstract

Carbon-13 NMR and IR investigations were carried out for adsorption of acetone on partially dehydroxylated and on methylated silica gel samples. The appreciable downfield shift for the carbon-13 resonance line of the CO group on partially dehydroxylated silica gel (ca. 9 ppm with respect to adsorption on methylated silica gel at higher coverages) and the shift of the IR stretching vibration band of the surface hydroxyl groups ( Δ v ̄ OH = 370 cm −1 ) are due to a strong interaction of the acetone molecules with the surface hydroxyl groups. The four IR bands observed for the CO stretching vibration of acetone adsorbed on partially dehydroxylated silica gel are ascribed to interactions with geminal OH groups, with isolated (free) OH groups, with nonhydroxylic adsorption sites, and to the gaseous state. The number of interacting sites evaluated from the NMR shifts was 1.4/nm 2 and 0.3/nm 2 for partially dehydroxylated and methylated silica gel, respectively.