Phase Transitions, Hydrogen Bond and Crystal Dynamics of p-Methylbenzyl Alcohol as Studied by Single Crystal X-ray Diffraction and 2H NMR

Abstract

The title compound (pMBA) was found to undergo a first-order phase transition at 211 K (Tc1). Another transition with subtle enthalpy change appeared at 172 K (Tc2). Crystal structure determinations at various temperatures revealed that the transition at Tc1 was accompanied by remarkable changes in the molecular conformations around the CH2-C and O-CH2 bonds and a reversal of the direction of the O-H O hydrogen bond. Experiments of 2H NMR were carried out on pMBA-d where the hydroxyl hydrogen of pMBA was selectively deuterated. Analyses of the 2H NMR spectra and the temperature dependence of T1 of the 2H NMR indicated occurrence of jumping motions of 2H between asymmetric potential wells at temperatures lower than Tc1