Structural X-ray study of dichloroalkanes

Four members of the dichloroalkanes series CnH2nCl2 (where n = 6, 8, 10, 12) in the liquid state were investigated by X-ray diffraction using MoKα (λ = 0.071069 nm) radiation. Angular distributions of X-ray scattered intensity were measured, and differential radial distribution functions of electron density (DRDFs) were calculated. The mean distances between the neighbouring molecules and the ranges of the spheres of intermolecular ordering were found. The mean coordination numbers were obtained from the area delimited by the minima of the DRDFs, and their dependence on the length of the methylene chain is also presented subsequently. On the basis of the DRDFs, the average free volume of the molecules and total free volume of the liquids were calculated. A relation between the structural parameters of the liquids determined from the experiment (arrangement of molecules in spheres) and their physical and chemical parameters (such as macroscopic density and electron density) has been confirmed. A simple model of short-range arrangement of the molecules was proposed, which seems to be valid for other polar substituted alkanes derivatives in the liquid phase. The results of the study of molecular correlations in liquid dichloroalkanes may be important for explanation of mechanisms of certain physical and chemical processes taking place in similar systems (e.g., diffusion or thermal conductivity).