Infrared study of the adsorption of anisoles on silica immersed in heptane

Abstract

Infrared spectra have been reported of silica immersed in solutions of anisole, six substituted anisoles (4-nitro, 4-chloro, 4-bromo, 4-methyl, 2-fluoro and 2,6-dimethyl), nitrobenzene and 4-nitrotoluene in heptane. Surface silanol groups were perturbed by hydrogen bonding interactions with either methoxy-groups or the benzene nuclei of adsorbed anisole molecules. Electron with drawing substituents in the anisole ring weakened both types of interaction. The proportion of perturbed silanol groups involved in interactions with benzene nuclei decreased with increasing electron withdrawing power of 4-substituents. Surface silanol groups formed hydrogen bonds with the nitro-groups of adsorbed nitrobenzene and 4-nitrotoluene molecules. An adsorptive interaction involving hydrogen-bond acceptance by nitro-group probably also occurred for 4-nitroanisole.