Density and temperature effects on the hydrogen bond structure of liquid methanol

The hydrogen bond structure of liquid methanol was investigated as a function of pressure and temperature up to 2.8 kbar and from 297 to 413 K. Chemical. shifts of the CH3 and OH groups were monitored throughout this pressure and temperature regime, and the chemical shift difference between these two groups was used to describe changes of the hydrogen bond network in methanol. The hydrogen bond equilibrium was investigated using molecular dynamics simulations and a phenomenological model describing clustering in liquid methanol. Results are presented concerning the size and distribution of hydrogen-bonded clusters in methanol as a function of pressure and temperature. The results indicate that the extent of hydrogen bonding decreases upon an increase in temperature. The results for pressure are equivocal, the phenomenological model suggests that hydrogen bonding decreases with increasing pressure, which supports earlier interpretations regarding the measured self-diffusion coefficients in deuterated methanol as a function of pressure. The molecular dynamics simulations, however, show an increase in hydrogen bonding with increasing pressure.