ARE THERE HYDROGEN-BONDS IN SUPERCRITICAL METHANOL AND ETHANOL

We report chemical shift measurements of the hydroxyl protons in metha nol and ethanol up to 450 degrees C and over a wide range of pressures . The extent of hydrogen bonding compared to room temperature conditio ns is obtained for the alcohols. The results are compared with our pre viously reported ones for water. Surprisingly, all three substances sh ow very similar behavior when compared on the basis of reduced thermod ynamic variables. Compared to the room-temperature situation, an exten t of hydrogen bonding eta of about 30% prevails for all three substanc es at near-critical conditions. The density-reduced extent of hydrogen bonding eta/rho reveals that the alcohols form hydrogen-bonded aggre gates already at low, gaslike densities. The temperature dependence of the data, extrapolated to a constant liquidlike density, implies enth alpies of hydrogen bonding of 12.8 and 16.8 kJ/mol in methanol and eth anol, respectively.