Usefulness of the Free Length Theory for assessment of the self-association of pure solvents

Densities and sound velocities in triethyl phosphate (TEP), N,N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile (AN) and methanol (MeOH) have been measured at the temperatures ranging from 294.15 to 333.15 K. The Free Length Theory (FLT) in its basic form has been used to assess the self-association of pure solvents at a wide temperature range. Detailed discussion and the criticism of the concepts of the FLT have been presented. As an alternative, the analysis of the temperature derivatives of molar compressibility coefficients and molar volumes has been proposed.