Infrared study of the adsorption of aromatic molecules onto silica and chlorinated silica. Application of the charge-transfer theory to the data

Abstract

The charge-transfer theory of Puranik and Kumar for hydrogen bonding is applicable to the hydrogen bonds formed between a variety of aromatic adsorbates and the silanol groups of both silica and partially chlorinated silica, with the predictable restrictions. From the relative positions of the respective data points in the diagrams correlating either the ionization potentials or the Hammett substituent constants with the infrared spectroscopic data, it can be concluded that, besides benzene and the methylbenzenes, styrene and most halogenobenzenes also interact via their aromatic π-systems, whereas the fluorobenzenes form H bridges via the fluorine atoms. If there are three or more methyl groups in the benzene derivatives, dual site adsorption of those molecules (mesitylene, hexamethylbenzene) must be taken into consideration.