Nuclear magnetic resonance relaxation, permittivity, viscosity and ultrasonic velocity measurements in binary mixtures of methanol and tetrahydrofuran

Abstract

Proton NMR relaxation rates of CD3OH and proton and oxygen-17 NMR relaxation rates of CD317OH with 6, 11.7 and 26.8%17O enrichment have been measured in binary mixtures with deuteriated tetrahydrofuran ([2H]THF) containing 10, 20, 30, 50, 60, 75, 85 and 95 mol% methanol at 288, 298 and 308 K. Deuteron NMR relaxation rates of CH3OD have also been measured in tetrahydrofuran (THF) at the same compositions and temperatures. From the measured proton relaxation rates, the 17O-induced intramolecular proton relaxation rates have been extracted. Using these values, the rotational correlation time (τOH2) of the OH bond of methanol has been determined at various compositions. The variation of τOH2 with composition indicates that the hydrogen bonding (self-association) of methanol begins to break up after the addition of ca. 25 mol%[2H]THF and at >40 mol%[2H]THF the structure breaking of methanol becomes much more pronounced. Negative values of the excess isentropic compressibility (KEs), excess permittivity (IµE), excess viscosity (ηE) and excess volume (VE) of CH3OH–THF mixtures over the whole composition range also indicate strong structure breaking, especially in the range 30–60 mol% THF, where all these excess parameters pass through a minimum. Proton NMR measurements also confirm that structure breaking of CH3OH by THF is stronger at >40 mol% THF. The deuteron and 17O quadrupole coupling constants of methanol in various CH3OD–THF and CD317OH–[2H]THF mixtures have been evaluated and a strong variation of the deuteron quadrupole coupling constant with composition and temperature as compared to that of 17O is observed.