The temperature dependence of the hydroxyl deuterium quadrupole coupling parameter and the rotational correlation time of the OD internuclear vector in neat ethanol-d₁

Abstract

The temperature dependence of the hydroxyl proton chemical shift and deuterium quadrupolar relaxation time of neat ethanol were measured over the temperature range 190–350 K. The proton isotropic chemical shift varies from 6.2 ppm at 190K to 4.7 ppm at 350 K. The deuterium NMR relaxation time in ethanol-d₁ varies from 6.2 ms to 309 ms over the same range. Ab initio calculations performed on various ethanol clusters ranging in size from monomer to hexamer show a linear correlation (R² = 0.99) between XD, the deuterium quadrupole coupling parameter, and δ_H, the isotropic proton chemical shift in ppm relative to TMS: XD(kHz) = 297.60 − 15.28δ_H. The temperature dependence of XD ranges from 199.5kHz at 190K to 221.4 kHz at 350 K. Using the values for XD and the relaxation time data, the temperature dependence of the OD rotational correlation time was found to vary from 282 ps at 190 K to 4.5 ps near the boiling point (350 K). Using these correlation times and bulk viscosity data, the Gierer-Wirtz model predicts a supramolecular cluster volume of about 317 ų, the approximate volume of a cyclic pentamer cluter of ethanol molecules. The cluster volume was nearly constant from 340 K to about 290 K.