Pressure and temperature dependence of hydrogen-bond strength in methanol clusters

Using 1H NMR spectroscopy, the hydroxyl proton chemical shift δ of methanol solved in carbon tetrachloride at methanol mole fractions ranging from 0.01 to 0.20 was measured at 20°C and 40°C under pressures up to 2000 bar. On the basis of a simple monomer–tetramer equilibrium for methanol molecules, it was possible to separate the effects of hydrogen-bond strength and extent on the chemical shift δ. Analyzing the pressure and temperature dependence of the chemical shift of tetramer methanol clusters, a pressure-induced strengthening and a temperature-induced weakening of hydrogen bonds in clusters of methanol molecules is found.