Intramolecular reorientations and the effects of thermal history and hydrogen bonding in four closely related organic molecular solids

Abstract

We have measured proton spin—lattice relaxation rates at 30 MHz from 77 to 330 K in para-di- t-butylbenzene, 2,5-di- t-butylphenol, 2,6-di- t-butylphenol, 3,5-di- t-butylphenol and modifications of the latter two in which the hydroxyl proton has been replaced with a deuteron.The observed maxima in the relaxation rates are interpreted in terms of the reorientations of the t-butyl groups and their constituent methyl groups. The observed relaxation rate depends, to some degree, on the thermal history of the samples and in the phenols this is attributed, in part, to the formation of dimeric and polymeric forms via intermolecular hydrogen bonding forming OH... O bridges. Infrared spectra are run with the three phenols in both the dilute liquid and solid state and the results interpreted in terms of hydrogen bonding. Nuclear spin relaxation due to the flip-flop of the hydroxyl proton is observed in 2,6-di- t-butylphenol but not in 3,5-di- t-butylphenol as expected on the basis of the IR spectra.