Proton NMR Chemical Shifts in Organic Liquids Measured at High Pressure Using the Diamond Anvil Cell

Abstract

Chemically-shifted proton NMR lines of organic liquids, including glycerol, methanol, benzyl alcohol, and 1,2-propanediol, have been resolved for the first time in the diamond anvil cell (DAC) at pressures up to and beyond 10 kbar. The change of the chemical shift difference between two closely-spaced groups of lines, one arising from the hydroxyl protons and other arising from protons in the backbone, was measured as a function of pressure in both glycerol and 1,2-propanediol. Deshielding of the hydroxyl protons relative to the backbone increased approximately linearly with pressure at the rate of 0.06 ppm per kilobar for glycerol, and 0.04 ppm per kilobar for 1,2-propanediol. These experiments prove that line broadening arising from a spatially inhomogeneous magnetic environment surrounding the sample in the DAC need not preclude NMR studies at moderately high resolution (1 ppm). This opens new regions of very high pressure for the study of liquids by NMR.