MOLECULAR-REORIENTATION IN THE PLASTIC CRYSTALLINE PHASE OF TRIS

Carbon-13 n.m.r. spectra of tris(hydroxymethy1)aminomethane (Tris) have been measured between 407 and 461 K. Proton-decoupled 13C n.m.r. spectra of solid Tris between 407 K and its melting point are relatively sharp (v1/2 < 30 HZ) indicating rapid overall molecular reorientation in this temperature range. It was not possible to detect a I3C n.m.r, signal for Tris below 407 K. The observed 13C n.m.r. spin-lattice relaxation times appear continuous across the solid ↔ liquid phase transition. From the temperature dependence of T1, a rotationaI activation energy of 51·6 ± 6 kJ mol-1is calculated, which indicates that the molecules must expend considerable energy in reorienting. The n.m.r. results are discussed in relation to previous differential scanning calorimetry and X-ray diffraction data which indicate that Tris undergoes a solid ↔ solid transition at 407 K. © 1979, CSIRO. All rights reserved.