Self-Diffusion Coefficients of Coumaric and Caffeic Acids in Tetrachloromethane–Acetone-d6 Mixtures

The self-diffusion of p-coumaric and caffeic acids in a binary tetrachloromethane–acetone-d6 solution at low concentrations of the dissolved compound is studied via pulsed field gradient-spin echo ¹H NMR at 278 and 298 K. According to the results, the self-diffusion coefficients of caffeic acid are lower than those of p-coumaric acid. The hydrodynamic radii of the acids in tetrachloromethane, calculated using the Stokes–Einstein equation, are lower than those in acetone-d6. This behavior is due to an increase in the degree of acid–acetone heteroassociation. Molecular association is also apparent from changes in the chemical shifts of protons in carboxyl and hydroxyl groups within molecules of the studied acids.