Influence of Cl...π interactions on adsorption of chlorohydrocarbons of various structure on graphitized thermal carbon black from the gas phase

Thermodynamic characteristics of adsorption of hydrocarbon molecules with the linear, planar, and cage structures and their isostructural chlorine derivatives were determined by equilibrium gas adsorption chromatography on columns with graphitized thermal carbon black in the range of the lowest concentrations of the adsorbate in the gas phase (Henry’s region). When the planar molecules of methylbenzenes and chlorobenzenes are adsorbed, the methyl groups and chlorine atoms, which are close in polarizability, make the same contribution to the heat of adsorption. However, in the adsorption of bulky molecules, the replacement of the methyl groups by chlorine atoms results in an average increase of 4 kJ mol−1 for the heats of adsorption. A possible reason for the differences in the heats of adsorption of the bulky hydrocarbons and isostructural chlorine derivatives is that induction interactions R-Cl...π(graphite) are imposed on dispersion interactions characteristic of adsorption on the graphite-like adsorbents. The induction interactions developed are due to specific features of the orientation of the R-Cl polar bonds in the bulky molecules of the adsorbates relative to the planar graphite surface at the adsorption equilibrium.