Self-Diffusion and Molecular Association in a Cyclohexane–Methanol Binary System at Temperatures of 298 and 323 K

Self-diffusion in a cyclohexane–methanol binary system was studied by the pulsed gradient spin-echo ¹H NMR method at temperatures of 298 (in the region of limited miscibility) and 323 K (over entire composition of the mixed solvent). According to the data obtained, the concentration dependences of the self-diffusion coefficients of cyclohexane increase with methanol concentration. However, the concentration dependences of the self-diffusion coefficients of methanol have minima. At the same time, according to ¹H NMR data, the chemical shift of OH protons in the methanol molecule decrease with increasing cyclohexane concentration and temperature, which indicates a decrease in the degree of methanol self-association in the system. The effect of molecular association on methanol self-diffusion in the binary system was evaluated using the Stokes–Einstein equation. The concentration dependences of the relative effective hydrodynamic radius of methanol were shown to have maxima.