Determination of molecular structure parameters from gas adsorption chromatography data. Part 1.—Determination of potential barriers to internal rotation in biphenyl

Abstract

The determination of the parameters of the internal rotation potential function W for an isolated biphenyl molecule (the equilibrium angle, α_min, and the potential barriers for planar, W₀₁, and for perpendicular, W₀₂, conformations) on the basis of experimental values of Henry's constant K₁(the retention volume for zero sample size) for biphenyl adsorption on graphitized thermal carbon black (GTCB), has been investigated. The atom–atom approximation for the potential function of intermolecular interaction of biphenyl with GTCB as well as molecular-statistical calculations of K₁ were used. The experimental values of K₁ do not permit unambiguous determination of all three parameters of W. If, however, one uses the value α_min= 42° obtained by electron diffraction, the experimental K₁ values determined at different temperatures make it possible to obtain W₀₁ and W₀₂. They are ≈ 7 and < 1 kJ mol^–1, respectively. Possible errors in the assumed dependence of W on the angle α of internal rotation and in the dependence on α of K₁(calculated by the molecular-statistical method) have but a small effect on W₀₁ and W₀₂ determined by this method.