Nuclear magnetic resonance spectroscopy and relaxation in molecular solids containing isopropyl groups. Part 2.—The large two-phase temperature region in 1,4-di-isopropylbenzene

Abstract

We report a proton n.m.r. study of the large, long-lived two-phase temperature region in 1,4-di-isopropylbenzene (DIB). The proton spectra are characterized by a narrow line superimposed on a 42 kHz broad line. The narrow line shows the chemical shift structure of DIB. When the sample is in the solid state the narrow lines are sharp (<30 Hz) near the melting point of 256 K and they broaden to ca. 1.5 kHz at ca. 170 K where they disappear. A variety of selective and non-selective Zeeman relaxation experiments as well as a Goldman–Shen exchange experiment were performed. It is concluded that the two sets of spins do not communicate on any timescale shorter than the spin–lattice relaxation times. The most likely interpretation of these results is that macroscopic pockets of molecules undergoing liquid-like motions are maintained in the solid, even 90 K below the melting point.