Low Temperature Specific Heats: III. Molecular Rotation in Crystalline Primary Normal Amyl Ammonium Chloride

Abstract

The heat capacity of primary normal amyl ammonium chloride was measu red between 20° and 280°K. If the substance is quenched to 90°K a metastable form is obtained which upon heat ing above 165°K slowly changes toward an apparently st able form. Two regions of gradual transition were found. X-ray powder diffraction photographs taken above and below the transition regions were remarkably similar. The experimental results are interpreted on the basis of rotation of the NH3C5H11+ groups in the crystals.

1H nuclear magnetic resonance, differential scanning calorimetry, and electrical conductivity studies on the phase transitions of pentylammonium chloride and the cationic self-diffusion in its rotator phase

“…Transition enthalpies determined on the warming runs of the DSC measurement for the sample cooled by three different methods are shown in Table 1 together with the reported data of the heat capacity studied by Southard et al, (9) as well as those of DSC by Tsau and Gilson (1). The heat anomaly observed at 238 K on warming the sample in the DTA measurements could not be observed in our DSC experiments.…”

“…They reported that, when the sample was rapidly cooled to 90 K, a metastable phase was obtained and was slowly transformed on heating into a stable phase above 165 K. Consequently, they concluded that the transition observed at 222 K is that between the metastable and stable phases. On the other hand, Tsau and Gilson (1) determined by Southard et al (9). Furthermore, the transition enthalpy measured by DSC turned out to be several times larger than those of the old study (9).…”

“…On the other hand, Tsau and Gilson (1) determined by Southard et al (9). Furthermore, the transition enthalpy measured by DSC turned out to be several times larger than those of the old study (9).…”

“…[CH2I4.NH3C1 (hereafter abbreviated to (pna)Cl), the room-temperature phase (abbreviated to RTP) is also a rotator phase (9), being isomorphous with that of a' of (pra)Cl as shown in Fig. 1.…”

“…Southard et al (9) measured the heat capacity of this salt and found two phase transitions at 222 and 246.5 K, and the appearance of some unusual thermal behavior at low temperatures. They reported that, when the sample was rapidly cooled to 90 K, a metastable phase was obtained and was slowly transformed on heating into a stable phase above 165 K. Consequently, they concluded that the transition observed at 222 K is that between the metastable and stable phases.…”